L2S, you have to think IDPA rules, which contrast greatly to USPSA freestyle.
If you leave a round in the chamber you must perform a tactical reload whereby you retain your otherwise empty mag (say in your vest pocket). It is exponentially faster to shoot to slide-lock and reload than bother with retaining the magazine.
Ok, I understand the rule I think, but why would that type of reload be considered "tactical"? It seems quite silly to pocket an empty mag, and "silly" is the PC word I can use on the forum.