An acid wash is used to roughen the machined surface with the goal of improving osseointegration. Chemical etching may be used in combination with grit-blasting.

Perceived advantage is a microscopic increase in surface area which may be attractive to osteoblastic activity. There may be a resultant increase in mechanical locking of the implant in the bone. To date, there is nothing that proves this to be a superior surface for a dental implant.

None, except for the possibility of contamination which I have not seen....

Acceptable provided contaminants have been totally removed from the surface.