I don't use spurs. If you saw me ride, you would know why.
Riding ability aside, the only horse I've got who might be OK with spurs is the little mustang. My gelding was spurred quite viciously before coming to us, and still has a large scar on one side where the hole healed, but the hair hasn't fully grown back. (The hole on the other side healed better). With him, I normally just make a kissing sound to go faster. For a walk to canter, kissing plus a squeeze with the calves. The key to getting Trooper to respond is to be as light as possible with the leg. Turns use very light pressure with the calf. I don't think my heel has touched his side for over a year.
My mare MIGHT someday be able to respond to spurs, but I can't really imagine her needing them. When she isn't scared, she is intensely focused on her rider and communication isn't a problem. When she is scared, she is scared. Not disobedient, but scared and not thinking well. When scared, she needs reassurance and a chance to unwind a bit. Her fears are totally real to her. I've just spent 3 months working with a trainer to help her handle her fears in an acceptable way. Using spurs, a crop, or even kicking hard to 'force' her when afraid could undo 3 months of training in 5 minutes. And for her, there are only two settings. Not scared = focused on rider, very sensitive. Scared = trust her rider to care for her, or meltdown.
If I was a better rider, the mustang could probably benefit from spurs. He's level-headed, but stubborn. Right now, he doesn't believe in subtle cues. However, I haven't had him long, and have been busy with the other two horses. I think I can train him to be more responsive.
I think a lot depends on how much you expect out of your horses. For the riding I do, I don't need a ton of cues. Left/right. Move laterally. Chill. Accelerate. Ease off. Stop. Accelerate a lot. That pretty much covers what I need my horses to know. That level of riding doesn't need a lot of refinement. I'd eventually like to teach the mare low jumps (1-2 feet), but none of them are built well for jumping, and my bones are getting a bit old for falling.
So for me, spurs may never make much sense. For others, spurs can be awesome.