It depends on the food. I love pre-chopping smoothie ingredients and freezing them in little sandwich bags so that in the morning I can just pop them in the blender, add a little milk, and I'm good to go with a nice cold smoothie.
I'm really trying to get a bit healthier with our meals so I'm starting to pre-chop a lot of stuff. Last night I was chopping pumpkin for a salad so I chopped the whole thing so I have no excuse not to put some in the casserole tonight...I did end up with orange fingers though! I'm also going to pre-chop ingredients for omelettes so that I have stuff prepared for a very healthy breakfast or quick and easy dinner.