I change my setup regularly. I tweak saddle height, fore aft and stem length/drop more commonly than say, cleat stance, saddle choice or bar width/reach, though each gets their turn for refinement as needed. For me its usually a factor of form; the more time i spend in the saddle, the more i also spend off the bike being cognizant of my posture and flexibility which in turn promotes changes to my setup. The key is leaving enough time for adaptation. My sweet-spot is around 300 km's with at least one exhaustive, high volume ride. I'm not looking for perfection, rather just fond of being introspective and enjoy validating my hypothesis.