It's a Sunday morning, halfway between Marathon, TX and Big Bend NP, out in the desert when an outside rear tire lost its tread. No cell service. Before I could get pulled over and out the door to inspect, a Border Patrol truck was alongside me. He radioed to dispatch my GS ERS card info and contacted them. 3 1/2 hours later a repair guy shows up. I had dropped the spare and had the rear of the motorhome up on its jacks when he arrived. A half hour later I was back on my way to BB NP. If I had not had a spare, I don't know how I would have communicated that with the repair guy.
P.S. At one point I considered changing it myself since I carry a lot of tools. However, I could not find the right size socket for the lugs, which is 15/16". I now have one. Wouldn't leave home without a spare.