No discussion about safeties on handguns would be complete without addressing the two that seem to cause the most controversy: grip safeties and magazine disconnect safeties. Although over the years several different pistol and revolver designs have utilized grip safeties, the primary one found in police service is the John Browning designed Colt Model 1911 and its clones.
Donald B. Bady, in his excellent and very detailed book, Colt Automatic Pistols (the second edition of which was published by Pioneer Press in 2000), reveals that the initial appearance of a grip safety on the military Colts was at the request of the U. S. Army, in its 1907 trials of the then experimental .45 caliber service pistol. Reports from the time indicate that the U. S. Cavalry representatives distrusted the safety of the proposed auto-loader during horse-back operations. They were concerned about cocking and decocking the pistol one-handed, with a live round in the chamber. One report stated that a horse had been accidentally shot when it stumbled while its rider had the pistol in hand. They wanted an automatic safety. This eventually evolved into the style we take for granted today on the 1911 model. Interestingly, there was no requirement that the 1907 model have a manual thumb safety, which also became the accepted standard for "cocked-and-locked" carry of the 1911 style pistol. However it evolved, the venerable 1911s are the most common representative of the grip safety idea. Of more recent design, the Springfield Armory XD and XDm pistols incorporate a version of the grip safety, which not only disables the trigger mechanism, but also locks the slide so that it cannot be manipulated unless the grip lever is depressed. The big question, however, is whether something that has been around for so long is really useful or necessary.
Many proponents of the 1911 style pistol don't seem to think so. For example, the late Col. Jeff Cooper, perhaps the foremost proponent of the superiority of the 1911 pistol as a combat and self-defense firearm, advocated pinning the grip safety down. If the safety wasn't fully engaged, it could disable the gun at a critical point in a gunfight. In fact, there are several different designs of grip safeties that incorporate bumps or ridges to ensure that the safety does indeed get fully depressed, even if your grasp of the gun is not perfect. This sometimes happens if your grip involves the thumbs forward or high thumbs style advocated by some instructors. Curling your gun hand thumb down brings the drumstick of your thumb into better contact with the backstrap of the gun, more positively depressing the safety.
Regardless of your grip preference, it seems to me that the grip safety has simply outlived its usefulness and serves no real purpose on a modern combat handgun. If anything, it is just one more thing to go wrong in the midst of a gunfight. That said, I still like my 1911s and my Springfield XDs and the presence of the grip safety has never been a problem for me. I just can't say it has ever been a help, either. Most unintentional discharges of 1911 style pistols occur during drawing or holstering. In either case, you already have a proper grip on the pistol, so the grip safety is deactivated. If you are careless enough to also have your finger on the trigger at that point, all that stands between you and a potential disaster is the manual thumb safety. If, of course, you remembered to engage it.
A grip safety seems designed primarily to prevent the user from accidentally firing a pistol with a relatively light, single action trigger pull, like the 1911. On the other hand, a magazine disconnect safety is more useful in preventing an unauthorized person from firing the pistol. When the magazine is removed from the gun, it prevents the gun from firing, even with a live round in the chamber. It does this regardless of the presence of any other safeties. As a result, it can actually be useful on a combat/defensive firearm. Pushing the magazine release button acts like an "off" switch, as the magazine falls or is removed from the gun.