It's a good thing to carry a spare, you never know when a flat will happen. We don't get many flats, but when we do it's a good thing to have a good spare. Two years ago we got a flat on the fifth wheel after travelling about a 1/2 mile through a construction zone on the Alaska Highway. A rock worked its way into the tire.
If your tire gets damaged beyond repair, it can take many days to get a replacement up here as the tire shops don't usually have speciality sizes in stock. They need to order them in from the south. If you have your own spare, it can save time and money.