If I believe that my current tires have enough miles on them to last the trip, I carry no spare. If I don't think they'll make it, I carry one spare and have someone send me an additional tire as soon as I use the first spare.
Makes no sense. A spare tire is carried for emergencies. Not normal replacement of a worn out tire. In the US, Europe, parts of Asia, parts of South America, you will frequently come across bike shops on a tour. If a tire is wearing out, you buy a new tire before its 100% worn out when you come across a bike shop. Spare tires that are carried are used when the sidewall gets damaged from a rock or piece of glass. Or the tread gets a large cut in it. Or the bead just refuses to stay on the rim anymore. I had this happen on a tour once. Tire blew off a couple times and the bead would no longer stay on the clincher rim. Also not sure why you would monkey around with the hassle of having a spare tire shipped to you when you use the one you are carrying. Wouldn't it be a whole lot easier to just buy a new spare the next time you run across a bike shop. Next day probably?