Gunsite Academy teaches that once you’ve reloaded your handgun, you should point your thumb toward your chest and grasp the slide between your thumb and all four fingers. Then you should forcefully pull the slide to the rear and release. This will disengage the slide stop, and as the slide goes forward, it will chamber a cartridge from the new and fully loaded magazine you’ve just inserted.
Instructors who advocate using the slide stop as a slide release argue that it’s faster. It probably is. Others, like those at Gunsite, who teach releasing the slide by pulling it to the rear, suggest that pushing down on the slide stop with your thumb is a fine motor skill, and that fine motor skills can deteriorate when you’re under stress. They can and do.