Turns out clipless pedals no better than flat pedals
 

According to this Youtuber who cited a bunch of studies:
Next thing they'll tell us skinny tires are slower than wide tires!

Clipless pedals certainly make a significant difference in efficiency on a recumbent.

Easy answer is "sometimes"

As I sometimes ride in normal shoes, sometimes SPD, sometimes SPD -SL, sometimes I am on a hybrid, sometimes a roadbike, sometimes gravel bike, sometimes a MTB (the MTB is either hardtail or FS), sometimes I wear a helmet, sometimes I don't. Sometimes I carry 2 water bottles, sometimes 1, Sometimes I air up my tires, other times I air them down. Sometimes I wear gloves sometimes I don't, Sometimes I go hard, Sometimes I ride leisurely.

Sometimes clipless is more efficient, and sometimes it isn't, I once rode 60 miles on a hybrid in running shoes on flat pedals, I'll NEVER do that again, not on purpose anyways!

What's so bad about it? I've done a century and several rides over 60 miles (3 this year so far, the latest one was 90 miles, half of it gravel/fire road/single track/beach) on a hybrid in either thin sole sneakers or running shoes, on flat pedals, without any problems to speak of.

I have always preferred platform pedals because it allows me to wear any type of shoes or boots I want. Platform pedals with lots of pins are very secure and have a good grip. I have ridden centuries on platform pedals without any issues. Clipless are good for pro racing but they are pointless for commuting or recreational riding.

I always enjoy his science-based videos. Towards the end of this one he pointed out all the studies were on stationary bikes and didn't include climbing or sprints, and they pretty much focused on efficiency gained from pulling up on the pedal not being pushed down. I remember years ago being told measurements show no one (including pro racers) was really pulling up, but they were taking more weight off the pedal going up.

On my gravel bike I have dual sided pedals - I use the flats when riding with my wife at lower speeds on paved trails. or on commutes where I don't want to carry extra shoes or clip in/out every few blocks. Kinda like on the stationary bike at the gym, not much difference in my speed on those rides whether I clipped in or rode flat side on those rides. But, on the occasional hilly ride on less than perfect surface in sneakers on the flat pedals, I find my feet are all over the place and I am definitely slower climbing and overall speed on the same ride.

A lot of the science around why skinny high pressure tires are not always faster than fatter lower pressure tires came about when the tests started to be done on realistic road surfaces and rides simulations - would be good to see the same kind of tests here.

What's the best chain lube?, What's the best frame material?, What's the best tire and size?, Flat bars or drops? Flats, clips, or clipless?
Meh, ride what you want.

I've ridden clipless since the early 1990s. I know that their use makes a substantial difference in my riding. Aside from beach cruisers rented while on vacation, I never, ever ride bikes without some form of clipless retention. It makes no sense (to me) not to take advantage of the benefits that they offer.

Are we doing this again?

Seems like every few months somebody discovers a ‘ Hidden Truth’ about clipless pedals to confirm their preference for flats, and the rest of us are either industry dupes, or subjecting ourselves to unnecessary risk.

Why do you think this is so?

I used clipless pedals on my recumbent trike (and other bikes) for years, not for efficiency but rather to keep my feet firmly on the pedals. This is especially important on my trike because of the potential for foot suck. This past year, because of foot issues, I have abandoned clipless pedals. I just could not achieve a cleat position that did not result in pain, hot-foot, etc. after long rides. On the trike I mounted heel straps which work well. Anyway - I have not noticed any difference in efficiency.

Clipless is important on recumbents because you pedal less efficiently if your feet slide off the pedals. The higher the bottom bracket compared to your hips, the more important this becomes.

You know what’s really inefficient? Having your foot come off the pedal unexpectedly.

I hope it's true, as I tried clipless, and they just were not for me. Maybe it's because I'd ridden mtn.bike flats with pins for so long that I just feel more comfortable on them. It would seem to me, if it made no difference though, that pro road racers (at least some) would be using flats. Or maybe at the pro level, they make more of a difference than at my (recreational) level. The way I look at it--ride what ya like, carbon, alum, steel, clipless, flats, whatever your preference, and enjoy your ride!

Clipless are no better than flats at what?
Answer, it turns out that they were only assessing efficiency on a stationary bike. Fine I can live with that, yet its not why I always ride clipped in.
Number ONE reason I clip in is for safety. Feet slipping off the pedals when pushing hard will take you down.
Also being able to pull up may not be efficient, yet sprinting or hard hill climbing isn't about efficiency.
Also, talk to the track sprinters. Personally I'm putting my money on the guy who's clipped in to thrash any guy who isn't clipped in.

I recently had that happen to me with clipless. I had come to a stop at a stop sign. When I started my standing accelerating, I thought I had clipped in. I hadn't. My foot slid off of the pedal and I slammed my taint into the seat. I have had far more issues with clipless than flats.

I know people that ride extremely long distances on platform pedals, a.k.a. "infinite float." I have had problems with them. One time I noticed my knees were hurting and realized it was because I had placed my feet on my pedals all katywumpus. I have also pedaled for 20 miles one-legged because my knee got sore on a 400 km ride and I refused to make the call of shame. I don't recommend that, saddle sores. I feel that would be difficult on platforms.

I will continue to use my Speedplay Zeros up to about 120 rpm. Others may differ.

I too like to commute with pinned MTB platforms, and any efficiency improvements that clipless pedals may happen to give, were negligible for my shorter commutes and errand travels.

Disagree with this. I've commuted for years with clipless pedals and very much appreciate their utility and confidence they instill when i ride in all conditions, even on a simple five mile ride to the office (which I haven't done since March).

I agree this is a pointless argument, but I come at it from the opposite side--I literally can't use clipless because of a congenital defect in my right ankle. I should probably qualify that--I won't use them because I used toe clips when I was a teenager, and the stress on pulling up caused my ankle to become incredibly painful, I simply am not willing to run the experiment with clipless, especially because I know walking in the shoes even for a short distance would also probably wreck my ankles. So, I have been riding platform pedals for all of my life and I'm now 59.

Long story short, I see a lot of claims about the supposed inefficiencies and hazards of platforms (slipping off, bad feet placement, etc.) that I know from very long experience are not really valid, at least for me. As you say, a lot of these threads are platform users seeking to confirm their preferences, but I submit that there's at least as much energy put out there by people trying to confirm their own preferences for "clipless."

Use what you like and what you feel safe/comfortable on. I have no reason to care about it. I will counter BS I hear about platforms, but since I've never used clipless and never will, I really don't have a valid opinion on whether they're "better".

Makes sense, you spent the majority of your ride starting from a stop, so to prevent clip-in incidents, don’t use clipless pedals.

Much like another thread where’s the rider is debating converting to 1x because the front shifter makes his air horn button too far away. Apparently he uses the air horn more often than the front shifter.

Everyone rides their own ride, I guess.

I think I've had that happen once in 50 plus years of riding on platforms, and I just put my foot back on.

I would have to agree with you. I ride both flats and clipless, depending on the bike, and the ‘mission’.
None of the assortment of injuries and battle damage I’ve picked up through the years have severely limited my mobility, and I like to think I have a slightly above average set of bike handling skills, so I can take advantage of what clipless pedals offer.

I also understand that they aren’t for everyone.
So, yeah, I’m pro clipless, but I try not to proselytize.

I switched to pinned platform pedals a couple of years ago after a bad ankle injury. I've gotten used to them and my feet don't move around while pedaling. I like being able to ride in any shoe but I do miss the convenience of being able to easily lift the pedal to my starting position when I am stopped. And, I'm still as slow as I ever was.

Yep.

The problem is that for most people, "flats" means running/tennis sneakers with cheap pedals with no pins.