The only time I use a clicker is when I’m far enough away from the horse that he can’t hear a tongue click, which means that I don’t use a clicker very often.
Horses want a treat every time (and between times, and for less effort, and just for free) but that doesn’t necessarily mean they’re going to get one. Once the behavior is on cue we can go to a variable rate of reinforcement so that we don’t have to click and treat every time we give the cue and get the behavior.
So for hoof cleaning, for example, I’d first shape the behavior and put it on cue, and then I’d keep it on a 1:1 rate of reinforcement until the horse got pretty good at it, and then I’d move on to maybe clicking after cleaning two feet, then three, then all four. I doubt if I’d ever fail to give him a treat after cleaning all four, but I could if I didn’t have treats with me and just walked away without looking him in the eye.