Rooting gives you root level access to your phone. It allows you to customize the phone well beyond what Samsung and USCC allow on the "stock" level.
If you have never done it, I would suggest spending some time reading about it.
Wait for the official update (at this point, if they hold to their "announced" target, it will be out in the next 2 weeks) and if you decide you still want to root, then you can do it whenever you like.