I was envisioning a shoulder strap like you see on some rifles. I have an older shotgun that was originally my grandfather's. It is in a 50+-year-old zipper case, but has no strap. I wasn't sure what is typical.
if you are going to carry it, then yeah, use a sling. i have a sling on my bird gun, but no sling on my home defense gun. just a personal preference. they make shotgun slings that cinch around the barrel and the stock, in the event that you don't have studs. swivel slings are equally as easy to attach and remove if you do have studs.
bird, skeet, trap, clay pigeon, etc....probably not. You're rarely far away from your car or estate wagon. field hunting, pheasant, turkey, deer, etc ... possibly so, depending on location. patrol ... quite often, a sling is to a long arm what a holster is to a handgun.
I have a sling on my HD shotgun. My thinking is if I'm in a situation where I need both hands but don't want to give up control of the shotgun then I need a way to throw it over my shoulder. If I have to lean it up somewhere or lay it on the ground to allow me to use both hands then someone else could get control of it. I guess different people view it different ways.
All my shotties have a sling.... They are all hunting tools too. Fast Food... Deer, geese, Ducks, Pheasant, Quail.....