I encountered this yesterday on a rail trail. The distant part...5 miles or so from any parking lots so zero foot traffic. All bikes.
Passed a couple of group rides all with the flashing headlight strobe. It was like being attacked by Star Wars. It made it hard to figure out how many bikes there were, where they were going, where they were, etc. I mean 15 flashing strobes all at once, all out of sync, each one wobbling left and right at a different rate....
On the street....I run my flasher 100% of the time. 2 up front. 2 in back. No exception. I want to make sure I'm seen by cars who aren't looking for bikes.
On the sparsely populated trail with only bikes? Turn those off. It's not a disco.