Hey,
I just bought a 91 Celica GT-S in almost excellent condition with 156,000km. 5spd of course

Now to get it safetied i have to fix a hole on the exhaust piping. The hole is after the catalytic converter. But the guy i'm buying it from said he has a cat back exhaust that he bought and should arrive in a few days and he said he'll sell it to me. Will it benefit me any or should i just stick with the regular? And what does a cat back exactly do?
Thanks