Always ease the slide down on an empty chamber, never slam it shut from slide lock. A G.I. rack grade 1911 may do fine when you slam the slide on the empty chamber, but a gun with a tuned trigger and fitted barrel will do better without it. The jarring of the slide slamming down on an empty chamber can cause the hammer to follow and the sear nose to crash into the hammer hooks. Your trigger job will last longer if you ease the slide down. Further, the lower lugs on a match fit barrel take a lot of impact when they contact the slide stop, and without the buffering effect of the round feeding into the chamber, you increase wear on your barrel by slamming the slide on an empty chamber. It's not the end of the world if the slide drops on an empty chamber, but it's not a good habit to develop either. It is the sign of an amateur 1911 handler.