What Are The Perks To Jailbreaking My Iphone And If I Do It Can I Reverse It

I've heard that there are a lot of perks to jail breaking your iPhone. The only reason I haven't done it yet is because it voids the warranty. Can anybody tell me some of the perks to doing this? I've also heard that once you jailbreak your iPhone you can reset it to un-jail break mode and that they can't detect it in the store if you go to get it replaced. Is this true? And if it is can anybody show me how to reverse a jail break?