My MacBook Pro isn't able to go to sleep. As soon as I put it to sleep and pull the plug the system completely turns off. This is due to the battery problems I have. SafeSleep helps.

Normally when you close the lid the system suspends-to-ram. This halts processing and other energy draining procedures but it still takes up battery life.

With SafeSleep the system will suspend-to-disk. Eating up as much power as if it were completely shut down. The upshot is in battery savings, the downside is it takes longer to suspend/resume from disk than to ram.

Saving to disk is normally considered hibernation. So far I have to say my MacBook Pro wakes better from hibernation than it does regular sleep.

Via O'Grady's PowerPage