Sorry to be blunt, but if you've seen it talked about so much, why didn't you read about it?
Rooting a phone gives you the ability to go into areas of the phones programming that the manufacturer didn't intend to you to. You'll be able to delete unwanted apps that the carrier installed aswell as change many other aspects of the phone that you couldn't otherwise.
Rooting also voids the warranty on you're phone and if you somehow "brick" your phone by installing the wrong ROM or tweaking the settings wrong, Sprint is not obligated to replace it through warranty.
If you plan on rooting your phone I suggest you begin reading all you can about it before attempting.