Incidentally, I've been sleeping polyphasically for some time now. Of course, there have been no real studies done on polyphasic sleep and it must be taken on anecdotal evidence alone. However, I don't feel any ill effects after a year. My schedule is tamer than others, however; the Everyman 2 consists of a 4.5 hour core sleep and two 20 minute naps [0]. Schedules like Uberman (six 20 minute naps equidistant in time, every 4 hours), Dymaxion, Tesla, and other nap-only sleeps do not seem to be stable, at least for most people who are not genetically mutated to sleep less [1].
There are quite some pros as well, such as more time for one; instantly falling asleep (got rid of my insomnia); removal of substances such as alcohol, marijuana, and caffeinated drinks like coffee; and lucid dreams with nearly every sleep. The latter is very useful for me as I can test out ideas in dreams and see how they could fare, a sort of omnipotent virtual reality.
The fact that many think polyphasic sleep is only Uberman or other nap-based schedules with ~2 hour total sleep time is disappointing to see. There are other schedules on that site that are far tamer, such as Everyman 1: sleep 6 hours at night, one 20-min nap during the day, which you could do on a lunch break. There are whole gradations from 9 hours (two 4.5 hour sleeps, not necessarily reduction of total sleep time, but it gives better sleep for some) to Uberman or Tesla (~2 hour total sleep time), which by the way is not known to be stable over a longer time period, a fact that the polyphasic community willingly accepts.
It is particularly disappointing to see because, as another commenter said, I'd like to see more research on sleep and perhaps synthesizing its effects into a compound, but if people dismiss these alternate sleep schedules, we may not fully understand what the brain is doing during sleep, as fewer researchers are incentivized to study it, thinking it's just BS, which hurts the field overall.
I do wonder though if the main advantages of polyphasic sleep are that it enforces a more rigid structure than monophasic sleep; if you miss a nap, or you oversleep, you're done for. If one could enforce the same level of scheduling in monophasic sleep, I wonder if they wouldn't have the same advantage of increased time. It's too easy to make excuses with monophasic sleep however, saying that you'll just sleep after one more drink / turn of a game / line of code, so polyphasic sleep acts as an enforcer of such a schedule, and here is where its true strength lies.
Communities I've found helpful are r/polyphasic, and its related Discord server. There are many examples there of successful polyphasic sleepers who've maintained their (non Uberman or Dymaxion) schedules for years at a time. In particular, the user GeneralNguyen is a great resource.
[0] https://polyphasic.net/schedules/everyman/
[1] https://www.nih.gov/news-events/nih-research-matters/gene-id...