How does it help... what exactly?
I don't see much point in using hibernation, sleep or etc unless you're talking about a laptop running on battery. Personally I leave my comp on 24/7/365, and just have it set to turn the monitor off after 20 min. Of course, it's also running SETI@home whenever it's idle.
The main disadvantage that comes to mind with hibernation is that you have to give up a chuck of hard drive space equal to the amount of memory you have, since windows dumps everything currently in memory to the HDD when it hibernates.