I recall the famous gunsmith F Bob Chow's match guns were like that. Dropping the slide without pulling the trigger would cause damage in short order,From each other.
When the hammer is cocked, the top of the sear (#39) is sitting on the ledge at the front bottom of the hammer (#40). When the trigger is pulled the sear is pushed out of the way, which allows the hammer to fall.
Part of getting a very light "target" trigger pull is filing down both the edge of the sear and the ledge on the hammer so they are barely touching. If the gun is cocked, so the hammer ledge is sitting on the sear, when the slide slams down, the vibration could force the fear and the hammer apart, damaging that delicate mating surface.
If the trigger is pulled when the slide is released, the sear and hammer are not touching each other, so no damage can be caused.
But, as I said up the thread, this only applies to very light "hair trigger" target actions. Normal "carry-gun" actions do not have that delicate a connection, and the vibration caused by the slide slamming home will not cause them to bounce apart.
Very true, but the trigger is disconnected from the sear. The trigger is also disconnected from the sear if you insert a new magazine while at slide lock and allow the slide to slam home into battery without holding the trigger to the rear..Whenever you fire a 7 round mag, until it is empty the trigger is ...back... while the slide slams home into battery.