Well, I think some people food can be bad. My boy cats don't seem to be interested in people food very much. Drizzt once in a while will eat some bits of cooked chicken as a treat - otherwise he only eats his c/d and s/d. He's pretty healthy, too.
He does have FUS but it's well under control.
My other boy cat, Bachus, will eat a bit of meat once in a while - mostly chicken or turkey. He prefers cat food though, canned or dry.
The girls on the other hand, well, they'll eat almost anything!
So I have to be careful with other foods so they don't get sick.
Snack food like potato chips would be bad due to the salt and fat. They are attractive to cats though. But then, junk food is not good for humans, either! Processed stuff would be bad due to the high salt: look at the sodium content on processed foods like a box of macs and cheese. The pasta would be attractive to cats because of the cheese. My mom has to watch salt in her food so she can't eat many processed foods anymore but make it from scratch to avoid the salt. So I say if its bad for people its bad for cats.
A bit of cooked meat should be OK. Just be careful if you use meat from soup: I think that's how Cattie-Brie got her liver infection - a tiny bit of onion that stuck to a piece of chicken. I didn't realize onions were dangerous to cats...
I don't give my cats cat treats.