Definitely refinement. Flying changes example- with spurs, I can keep my mare straight and she changes right on cue.
No spurs, she twists (thinks I'm asking for travers), and changes late. All kinds of stuff.
My sister always told me that with spurs you can put 'buttons' on the horse- so THERE means leg yield, THERE means medium trot etc. Not sure how much sense it makes, but it works for me :)