Your Browser is Outdated
On most semi-automatic firearms the slide or bolt will stay in the rearward position when the last shot is fired and the follower of the magazine engages the bolt catch. This quickly lets you know the magazine is empty and allowed you to reload and then use the slide/bolt release to chamber the next round of the loaded magazine. It is not necessary to have for the firearm to work, but is a feature many shooters like.
Yes, that means no bolt being held back after last shot is fired. Aka non L.R.B.H.O.