Spurs can be great aids or abusive. It all depends on the rider AND the horse.
If you put spurs on my 9 yr old gelding... you'd be thrown. He is very sensitive. He will work a cow with the best cutting horses with just a squeeze of the calf... or run a 17 sec barrel pattern in a big arena without being pushed.
My filly on the other hand... you need spurs for anything serious. Usually if she knows I have them... I don't need them. But if I get on her without them... everything is sluggish... her spins, her stops, her sidepasses. So it really depends.
I do hate when people use them to make a horse run. It just slows them down. As Smrobs said.
Many people have sighed for the 'good old days' and regretted the 'passing of the horse,' but today, when only those who like horses own them, it is a far better time for horses. ~C.W. Anderson