I'd expect pretty much any move to make the customers do work that paid employees used to, increases customer theft (which, as noted elsewhere in this thread, is far from the only threat—employees, including managers and security, steal lots).

I mean, consider a classic old-school store (talking pre-supermarkets and pre-big-box stores) where a clerk would fetch what you wanted. Much harder to steal there. Save money by not paying enough clerks to handle that and making customers pick out their own stuff, and now customers can/do steal more.

Same with stuff like self-checkout, I'd expect. Might also increase the rate of honest mistakes resulting in accidental theft, though I've seen so damn many of those errors from paid clerks that I wouldn't bet on it.