Plenty of people would love to be able to do an iPhone 4S jailbreak. It’s been done on every single variant of iPhone released so far and people will keep doing it in the future as well. In most cases, people that do an iPhone 4S jailbreak will probably want to use another network than the one where they bought the phone. Since the phone is locked on the network for which it was bought, a jailbreak is necessary to use the phone that you paid for in any condition you want. This type of operation is usually known as unlocking for most other phones but for the iPhone it’s being referred to as a jailbreak.
Another reason why you might want to do an iPhone 4S jailbreak is to be able to install themes, tweaks or apps on your phone that Apple might not approve of. Since the iPhone is a closed system, normally you can only install apps from the official App store. With the help of a jailbreak you can install any app or game you want, even if Apple doesn’t approve of it. Since Apple is so picky when it comes to the apps you can install, there is a kind of a black market available where you can find all kinds of apps that normal iPhone users don’t have access to. All these apps are possible only if you do a jailbreak on your iPhone.
The main reason why people do a jailbreak operation on an iPhone is to be able to access other cellular networks than the original one. Since Apple negotiated with operators from around the world over the exclusivity of the iPhone 4S, if you don’t like the operator they decided to team up with, your only choice is to unlock the phone, so you can use your own favorite network with it.