As he said above: if you need to ask, you don't need to jailbreak it.
Apple claim it voids the warranty, but I doubt that's ever been tested in anger. If it doesn't work, they can't tell it's jailbroken. If it misbehaves, you can restore it to pre-jailbroken status.
Mine is jailbroken (as is the iPhone) because there is software I want to run that Apple don't approve of. The brick risk with those items is minimal. Messing with the innards may be more hazardous.