there are ongoing discussions about the effects of "popcorning" in grinders, and the effect it has on the grounds and subsequent shots. those discussions won't end until we get some serious grind analysis done. because there is the potential for popcorning to be a negative factor, and it's not very likely that it will be a positive factor, the prevailing attitude seems to be it should be avoided, especially in competition.
that said, i don't worry about it in day to day affairs. i chuck a scoop of beans in my cupping grinder and let 'em dance. the versalab grinder also seems to have no problems with it, but that might be a result of the dual burrset (i've got one on loan for awhile).
i can't see that it's hard on the grinder, except, perhaps, that the increased motor run time might cause cooling issues on mazzers. that's a tough one to judge w/o measurements, since the motor is really spinning under a very light load compared to a full-on loaded grinder.