Q: Benefits of Jailbreaking ?

I recently just picked up my iPhone 4 and everyone is talking about jailbreak.  I have been looking at alot of sites, but there is so much information.  This is my first iPhone and I was just wondering if someone could fill me in as to what benefits downloading jailbreak will give me.  As well, what are
the Negatives?  I cannot afford to replace this phone if something major happens, and I really am an amateur at this to go in and do some of the fixes that others are suggesting.  This all sounds interesting to me, but I want to have all of the facts before jumping in.
Thanks to all that will respond

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