putting the efforts in improving the function on one side and improving the aesthetic on the other side. Both achieve two very distinct targets.
Lot of functional surfaces could be left untouched straight from the machining, but polishing the contact points will improve the users' experience (setting, winding, chronograph) as well as the functions (drawing less power, keeping better timing) and durability (less wear off, less powder of metal going everywhere). Here is an example for a tirette that will be solicitated when changing from winding to setting. Both are totally functional but one will be more pleasant to use while generating less powder in the movement.
On the other hand aesthetic is really improved by creating contrasts with reflective and matte surfaces alternances. Creating lines, curves, textures...
Well, actually, some aesthetic finishing do have a function as well. Cote de Geneve is supposed to catch dust before it gets into the oil at the pivots. Anglage is supposed to avoid sharp corners with swarf that will spread in the mechanism later on...