While not disagreeing with any of the above answers. It does depend upon the purpose of the work.
Decorative work needs to be form and finish.
Replacement parts for antiques etc., need to match the rest of the piece, so if its a bit worn, a new knob, highly polished would look wrong.
Replacement 'Second Fit' parts for a house (e.g. stair banisters) must match the others to the eye, but probably need only sanding to 180 grit, to leave a tooth for the paint to adhere.