My subjective experience. A lot of time and distance on the bike in traffic, as it is my main (and practically only) means of transport, in addition to weekend joyrides. But still just one man, so not statistically relevant (hear-say category, objectivelly).
During the night, lights are a no-brainer. It's not a topic (and I sure hope we can all agree on that), but worth mentioning for one point - as
FBinNY mentioned: flashing rear light makes it easier for the drivers to notice you (there is a
difference between being seen, and being consciously noticed by the drivers).
Cars coming from behind are usually going straight towards you, and you are riding away from them (though usually slower than them). This give the drivers enough time to notice the flashing light, and the fact it is flashing makes it more likely for them to notice you.
For the front light, during the night, the situation is the opposite. Drivers pulling in from a side road have very little time to notice you (many don't look left-right twice, and the wide beams on the modern automobile windscreens can block your profile).
Because of that, it is possible & probable for the driver to be looking at you just during the split-second that your blinking light is in the off-phase (if you don't have another full-on light).
Also, the speed difference is increased by your speed (you are going towards the cars coming from your front side, not away from them), which also reduces the reaction time.
For those reasons, I think that you should have a full-on front light (and add a blinking one if you think it's a good idea), while for the rear, it's probably good to have a blinking one (even without a full-on light, though there too it sure is safer to have both).
Now for the day.
I have noticed that a blinking front light lets drivers notice me more often (cut me off less often when pulling in from the side roads).
That also helps when there's rain, fog, or a low sun shining from behind me.
My dynamo-hub light starts blinking when I slow down below 10 km/h (the main beam, while the daytime "position" LED stays full-on). That flashing does seem to draw drivers attention when I slow down (before an intersection, or when I see driver who is likely to do something silly).
Again, that's my subjective impression - I didn't do any stats or counts, as they make little sense for this kind of phenomena when tracking fewer than a few thousands of riders.
For the rear light, I can't really tell if it helps during the day. I can presume, guess, but I can't figure out when the drivers first notice me.
My dynamo-hub rear light shines a bit brighter when I'm braking (like automobile brake lights), and starts blinking (with a full-on LED) when I slow down below 10 km/h (at about ~6-7 km/h probably).
Not sure if that helps, but I suppose it does no harm.
Now, what
Leisesturm wrote about, well, basically common sense and caution - I very much agree.
I've been riding for decades without day-running lights, and managed to stay safe.
Lane positioning, looking in front and around you, making a "plan B" in case a driver does something silly - it all helps tremendeously, and without that, lights will not help.
Having said that, I do believe that daytime lights do make a tad of a difference. Say an extra few percent of chance for being noticed (on time).
So, for me, it boils down to whether it's a hassle to use.
With a dynamo hub and LEDs, it's no hassle whatsoever (at least for me).
I even mounted some dynamo lights on my "gravel" bike (the one I take into dust and mud on the weekends).
With batteries, I never bothered to use the lights during the day, unless it's raining, foggy, or the sun is very low.
Relja