Originally Posted by
WillBrink
Depends on who you ask. Some are in favor of them (as long as the design is robust) and some will not use any 1911 with them. They are designed to prevent the firing pin from moving unless trigger is pulled. Colt had the series 80 safety. S&W seems to use something of their own design that is "Schwart like" but not identical. Unlike Kimber, S&Ws internal safety has been very reliable.
On a 1911 without them, if you drop it barrel down at the right angle from a high enough distance, the mass of the firing pin is enough to make it strike the primer, and boom. Rare, but it has happened.
Springfield has solved the problem in an uber simple way: titanium pin with stiffer spring, no boom when gun is dropped straight down on the barrel from X height, which make purists happy with improved safety without adding additional parts that could fail.
I'm not a gun smith or engineer, so that's getting to the limits of my knowledge on that topic.
Read articles by Yam et al for much more details and far greater depth of knowledge.