Display sleep is good for several reasons.
When your computer is operating in the background, but your not at the computer for a short period of time, display sleep saves energy. Display sleep can also automatically lock the screen and require a password to unlock, protecting you from bad guys (or co-workers) who want to mess with your computer.
Putting your entire computer to sleep locks the computer, but does not let it operate in the background.
Dimming the screen with the brightness keys (F1 key) saves energy, but does not lock the screen and require a password to unlock.
I tried BetterTouchTool, but I had issues with clicks not registering, especially when I was trying to click-and-drag an item on the screen. So BetterTouchTool is not for me unless I can find a way to fix that issue.