Tread with care - this is an interesting, but poorly understood, area. If you take all your information from sites supporting polyphasic sleep, you may get an artificially favorable impression.
For example, consider the idea that it takes several weeks for the body to adjust, and “learn” to fall asleep quickly… bear in mind that we know, from extensive research, that being chronically sleep-deprived also results in going into REM sleep very quickly. This pattern is so well researched and documented that measuring time to fall into deep sleep is one of the standard diagnostic measures of the level of sleep deprivation.
So, if you partake of a new sleep pattern that reduces your sleep by several hours for several weeks, is your body “learning” to go to sleep quickly? Or is you body just falling asleep rapidly because you’ve been sleep-deprived for several weeks?
On the subject of REM versus other levels of sleep - REM sleep is closely tied to certain mental processes. It’s currently believed that it’s probably related to things like memory consolidation, processing the day’s events, etc., and we know that chronically disrupting REM sleep will lead to a variety of (mostly bad) psychological effects. Not only a REM-deprived person rapidly fall into REM when lying down to sleep (instant dreaming), but they are also likely to hallucinate if they try to stay awake.
But solving the need for REM by taking naps isn’t enough… REM is a small sub-segment of sleep, in terms of time spent. Light sleep and non-REM deep sleep are not perfectly understood, either, but they seem to have purposes. Your body’s physical recovery is dependent on time spent during those sleep cycles, and is likely unrelated to the amount of REM sleep. We have many circadian (daily) rhythms: while we sleep, we see dramatic changes in melatonin, cortisol, thyroid stimulating hormone, prolactin… and these appear primarily tied not to 24-hour cycles, but rather, tied to our sleep cycles. What is the impact on physical recovery of decreasing the amount of time spent in light and deep sleep? Impact on immune system?
True, there’s good evidence that polyphasic sleep patterns may have been more common and natural in our history as a species, especially seasonally… but there’s little evidence that those sleep patterns resulted in less total sleep than our current norms. In fact, humans already sleep considerably fewer hours than other primates, and sleep fewer hours than most mammals. I believe the only major groups of mammals that sleep fewer hours than humans are grazing animals, like cattle, elephants - these animals all have to eat for many, many hours a day, and they sleep by taking brief snoozes while standing. Other groups of mammals all sleep much longer, including those most similar to us (such as primates) and many that are very dissimilar - everything from mice and rabbits to cats and dogs all sleep more hours than we do.
But, now that we’re on the subject, I may do some more research (checking out the latest science) and experiment with polyphasic sleep, myself. But I’ll be splitting up my sleep time in hopes of improving health, not in hopes of decreasing time spent asleep. My goal is to increase the value (and wakefullness) of each waking hour, and to live as long as possible in excellent health. Also, I’m currently in a situation that allows for polyphasic sleep, so it’s a good time to experiment.
My personal experience suggests that those who don’t rest enough are generally functioning at inferior levels (compared to what they’re capable of), but that they can’t tell that they’re sub-standard, because their ability to tell the difference is one of the things most impaired!