It depends. I've got all my deer rifles scoped now, as well as my Mossberg shotgun. For me, it's not a luxury. I'm 52, and my eyes have gone to the point where I can't see the irons and the deer at the same time anymore. In fact, I've had to remove my last 1.5-4.5X scope and replace it with a 3-9X, because I just can't see deer like I used to.
Some shotguns come already drilled and tapped for scopes. With the Rem 870's, I think it depends. Some rigs have cantilevered barrels. If not, you can put a side-mount on an 870 that does not require a 'smith.
The important thing is what you're going to need to take a deer. As long as you can put a slug consistently into where you need without a scope, then a scope is unnecessary.