I think Santa Claus is, by and large, quite beneficial, for when the child is finally allowed -- or forced -- to recognize the nonexistence of Santa Claus, then the child is able to go through the vital intellectual process of reconstructing reality in light of new evidence, complete with back-forming new stories to account for past events. This prepares the child for many other disillusionments and gives her vital and well-supported experience in maintaining her grip on reality independent of the stories told to her at any given time.