Is there any difference between chopped and crushed garlic in cooking?
Chopped and crushed garlic have different flavors in dishes. The smaller the pieces the garlic is made into (with crushed being super small), the more pungent and bitter the flavors.  Several food bloggers have reported their experiments on testing the differences.  

This sounds surprising, but members of the Allium genus (which includes garlic, onion, leek ...) are booby trapped: around the cells there is a liquid that when combined with a chemical from the cell's interior creates a series of nasty sulfur compounds.  The more the cells are damaged and exposed to oxygen by cutting or crushing, the more of these sulfur compounds are generated.

If the garlic is fried, the size of the pieces also determines how much of it browns.  For crushed garlic this can happen before one has a chance to add more liquid to the dish, essentially burning the garlic and imparting a bitter taste to the dish.