What a good or bad thing to jailbreak your itouch or iphone?

Thanks!

You can do more with it, like get access to a new app market where the apps are free but it also makes your device somewhat slower.

Do you mean unlock it? If you do and you're doing it to use for a different carrier its illegal now, they passed a law. I know you call customer service or the phone company or the place that sells it. Like if it's a Verizon phone call the Verizon store. I'm not sure they will do it anymore, but you can try. If that's not what you're talking about the I have no idea.