Food processors (proper ones, not hand "choppers" and the like - those are nearly pointless) are a terrible replacement for basic knife skills.
What they are mostly great at is a few things that are so labor intensive (ever made hummus by hand?) you otherwise might not bother. Also a good time saver for things like pasta dough.
Good for making mayo and the like by hand and for thin slicing potatoes and carrots. The biggest issue for me is setup + cleanup >> use time for most cases.
