What's the pros and cons of jailbreaking my iphone 4s?

Should i jailbreak iphone 4s ios 6.1.2?

Lol. There are no "pros" for jailbreaking ANYTHING. Your phone will work for less than a week more, And then it will freeze and basically become garbage. Best part is you void the warranty so you can't get a new one for free or for a discounted price. Think about it.

The Pros: you unlock the true potential of your phone, you can get stuff for free, have tweaks that help your productivity, customize your phone, or any thing to make it "your" phone.
Cons: you void warranty of the Idevice but if you restore it, the warranty is good.

So answer #1 is clueless. You can restore from a backup making the phone revert to the way it was before the jailbreak. I've know people that have the same jailbroken phone for over 2 years. Oh and when you get a new phone the old one makes no difference when you renew your contract for a discounted phone. You keep the old phone.