negative. Less surface area, more pressure. The precision of the cue purely comes down to the horses understanding and has literally nothing to do with the tack you use or the amount of pressure you put on the horse. With that in mind, if you can't do it in a snaffle or even halter and without spurs then you shouldn't be doing it at all.
Now I do show in leverage bits and I wear spurs because it all looks traditional etc. but I will confidently say right now that if you believe "refinement" comes at all down to the tack you use then you're greatly underestimating your horses intelligence.
Perhaps I should have clarified my meaning.
Of course less surface area means more pressure if the rider applies the spur with the same intensity as they would/do with their heel. It's simple physics: same load applied over a large area vs a small area, and the pressure will be greater where the load is distributed over less area. I never said anything to the contrary. So, spurs apply a clearer aid by virtue (or vice?
) of upping the pressure and further localizing the application. Spurs are not tack, but an artificial aid, and allow less force from the to apply the same or more intensity of aid. I never said that if the horse doesn't understand the pressure that spurs magically train the animal.
Because a rider with spurs has the ability to apply pressure over, say, a half-inch square (as with my POW spurs) rather than approximately 2 square inches of heel pressure, several more things can be clearly asked of the horse in a smaller area, minimizing the movement of the rider's leg.
I don't know about everyone else, but when I do ride in spurs they barely touch the horse's side and I get the same result that a comparatively
firm touch of my calf gets. That comparatively firm touch is still very light, simply backing up and clarifying weight aids.
As far as "doing it in a snaffle/halter and without spurs" goes, I do it every day in a snaffle and without spurs, and also have good control bareback in a halter. Kindly do not mistake an understanding and appreciation for what correctly applied spurs allow for in terms of refinement and precision of aids for reliance upon them for refinement period. Spurs certainly do not refine anything - only an educated and efficient rider does that. I claim to be neither.
My apologies for adding to the off-topic-ness of the thread - I do have more to say on the topic of spurs and their correct use, but I need to be on the road in half an hour and stalls have to be clean first...