Strange question in a sub-forum which is all about hacking/jailbreaking iphone which has 33,471 threads and 309,498 postings.....
But i'm not talking about the older models. I can see reasons why you would jailbreak a 4 or a 3GS or a 3G or an original. I'm not seeing what there is to add on to a 4S.
EDIT:
Just stop... There are well over a few hundred tweaks that people use constantly while jail broken. My favorite is probably LockInfo. Apples notification center is a joke compared to this.
Also I love 5 icon dock, iblacklist, and many many more.
There's also countless threads talking about this. Read up to fight ignorance!
Okay I guess there are some good tweaks. I just don't see anything super amazing though (5 Icon dock? Is that really needed? and isn't LockInfo a paid app?)
Plus, it's the internet. I'm allowed to speak my thoughts.