Originally Posted by brad
The differences are tiny but effective.
Brad pretty much said it.
For me, I've taken out the brightness and contrast controls out my top menu, and I try my best to always use Curves. When I can't use curves (curves can be hard to understand), I'll use levels.
Brightness + Contrast = Axe
Levels = Knife
Curves = Scalpel
Keep in mind that non-destructive layer editing can be fine and dandy but for some things it's quicker and will save file size if you just press Cmd + M or Cmd + L.