Two pair of spd-sl shoes for the road bike, two pairs of spd mtb shoes for the gravel bike. That way if a pair gets wet, I can ride the next day while they dry out. Switching the next road bike to spd pedals, like others have mentioned, it's nice to be able to walk, and they're easier to use. I only went with spd-sl because that's what all the other roadies were doing. lol