Punching a cat is mean for a start.
Punching the cat guts out does not really have that many benefits.
For a start your going to cover the back of you car in black carbon which is very hard to get off.
Your going to going to see the occasional flame exit - not cool at in appropriate times i.e around the wrong crowd.
In terms of sound, I have heard it swinging both ways, louder and quiter. I assume it depends on exhaust modifications, engine mods, the type of engine etc.
And in terms of performance. Very little in an NA. There isn't a very large volume of gas exiting the engine. So minor things such as catelitic converters will have little restriction.