"Why We Nap" (ISBN 0817634622) is a great resource about polyphasic sleep. Most of us are in the habit of monophasic sleep, even if we have crazy or limited sleep schedules. The thing is, if your body goes through more than one sleep cycle in a period of sleep, then there is a period in the middle where you are basically not getting anything from the sleep. Biphasic sleeping is a way to reset the cycle more quickly, so instead of 2 hours of low value sleep, you just wake up for a half hour or so.
Personally, I've found that another important thing is simply sleeping consistently. That means either certain times of the day or for certain amounts of time. For example, always sleeping in three hours means your body knows what to expect and makes the most out of the time. Biphasic is just the easiest (and perhaps most natural) way to do it.