Well the whole thing is that sleep is something that varies by person, it always has. But biphasic seems to have become more popular because it works for more than just a few. You see, others as well as I find that if we sleep for 6 hours monophasically then after a few days we kind of crash and end up being tired so we oversleep the next few days and it turns into a cycle of 6 hrs 6 hrs 6 hrs 8 hrs 8 hrs 8 hrs 6 hrs 6 hrs 6 hrs etc. But with biphasic sleep, it doesnt happen, it is just 6 hours of total sleep everyday. Now it might not always be optimal for everyone, but when it is it is a good way to reduce time spent in bed.
The reason I decided to do it? I have to make international business calls to the UK. And so therefore when I wake up in the morning I am able to do that. The UK is 7 hours ahead of me so when i normally used to wake up at 7:00 and be ready to go by 8:00 it was already 3pm in the UK and when I have class at 8:00 it becomes very hard to contact people in the UK. This is why getting up around 5am is very helpful and in the evening around midnight my time is not wasted either, I market on the internet and read stevepavlina's site