I'm probably an outlier and may get lit up by my betters but I don't follow the "one to carry, one to shoot" philosophy.
I have two but I shoot one for few sessions, clean it, and rotate. Both guns get about the same number of rounds over time.
I have less trust in a gun that has been carried too long but not shot. Lubricant might start to dry or fail. Crud starts to collect.
I also think the gun that has been running great at the range, once clean, is the most "known good" gun.
Regular preventative maintenance is part of the routine, too. The clean gun with new parts becomes a range gun until I'm confident the new parts are ok. Then it's cleaned, moved to carry status, and the former carry gun gets the same maintenance. This keeps me from having to fuss over, "when is the last time you got a new recoil spring versus your brother?"
Bear in mind I'm talking about Glocks here and "wear and tear" isn't something I worry much about. Springs and small parts replacement, yes, but I don't see myself wearing out the frame, slide, or barrel.
I was also going down the "one to compete" route for a while. It ended up everything that I liked on the competition gun got put the carry guns. Everything that wasn't practical for carry got taken off the competition gun. So I ended up with 3 identical pistols. Wups.