I have been using spurs for decades. I no longer train young horses to saddle, but when I did decades ago I did NOT use spurs until I "needed" to for establishing further impulsion.
Now, when I am riding riding school horses I wear spurs for every ride. I have MS and every summer my riding teacher used to take my spurs off as I lost control over my lower legs. However I found the Spursuader spurs, and my riding teacher has let me wear spurs through two hot, muggy summers. The Spursuaders are great, there is no way I could poke a hole in the horse's side, severely bruise or tear the skin, and the horses accept them even when I am at my worst physically.
I apply the spur by turning my toe out, in accordance to the gait phase of the hind leg on that side. That method definitely does not look elegant, but any other way of applying the spur destablizes my lower leg making me much more insecure in the saddle. The spurs I use and the way I use them is completely determined by my physical limitations caused by the Multiple Sclerosis.