Pros and cons of jailbreaking?

I'm thinking of jailbreaking my iPhone, but am scared that it might mess up my phone altogether. What are some pros and cons of jailbreaking?

I'm not too sure about what the device is capable of when it is Jailbroken, but I do know that when you do Jailbreak it the warranty is no longer valid. So if you are gonna jailbreak it then wait for the warranty to go off.