It's mostly for show. It will protect you from a get-a-way grocery cart, and maybe someone backing into you. But that's what bumpers are for. Nissan bumpers are cheap, so putting a more expensive part to protect a less expensive part seems counterproductive.
If it was me. I would have had the dealer remove it and replace the parts they cut into to make it fit. Probably too late for that. If you don't want it, you could always put it up for sale, and use some of the money to order the parts they cut. They're plastic and cheap. (order from
www.xterraparts, your dealer probably would charge you too much).
Anyway, if it doesn't bug you, keep it. Just be aware if you offroad with it, it could potentially cause more damage than it's worth.