Best Setting For Sleep?

I'm wondering what is best, accept the default sleep settings, or change them? I set mine to sleep after 20 minutes, but default is longer. Does windows need to do things, like de-fragging and so forth, that will be adversely affected with a quicker sleep setting? Sometimes, my PC won't go to sleep after 20 minutes. I used to think there was something wrong with it and I would force sleep. Then I thought maybe I shouldn't do that, maybe it needed to do some routine maintenance or something. Should I change the settings to the default mode?

No thoughts on this? OK, I guess I'll conclude that going with Microsoft's default settings would be best.

Actually, after a little research, I decided to go with the EPA's recommendation: 15 minutes for screen, and 30 minutes for sleep.