The advantages are I fulfill all my night-owl hacking needs and have a good social life. And I can make any morning meetings by adjusting my first sleep to 4am - 8am.
Apparently before the invention of the light bulb, most people divided their sleep into two sections. The details are sketchy but there's widespread reference of "second sleep" throughout history. I think it was the sort of thing they went to bed at 9pm - 1am and then 4am - 8am.