I have had a CCW permit for many years. I have owned handguns for home defense for even longer. I was trained to use all kinds of weapons in the military over 30 years ago.
As a civilian, I cannot think of single reason where a weapon mounted flashlight (on a handgun) would be preferable to an unmounted light.
They don't fit in holsters (for the most part). They generally require fine motor skills that are lost in the stress of use in actual self defense conditions. They are small and not nearly as versatile as a handheld light, and they provide a target for a threat (which is true with any light, but a hand-held light can be manipulated in ways a rail mounted light cannot be)
Along with night sights, I think that they are a waste of money. I will never understand the popularity of night sights for self defense..they do nothing at all to illuminate a target - in fact in realistic self defense distances, I don't think sights are useful at all.... I practice shooting without sights for self defense. To me, sights are great for target shooting. Or hunting (I guess...I've never hunted for sport). I do target shoot, and for that, sights are essential. To hit an assailant 8 feet away in a life or death situation, I don't expect to have any time to line up sights. Or even the steadiness to try if I did have the time.
I think a comfortably sized hand-held flashlight is an ideal companion to a handgun for home defense. For concealed carry, a rail mounted light is going to require a holster that makes concealment even more difficult.
I've owned exactly one pistol with a rail on it (a Springfield XD9 SC) and I have since sold it. (not because of the rail, which was very small and only took specially designed lights and lasers for such a small rail anyway). A fine gun, but too bulky for concealed carry for me, not a fun range gun and I have better guns for home defense. So as good a gun as it was, it had no purpose for me.
As a law enforcement officer, or a combat soldier, then the reasons for light rails become obvious and useful. Even necessary.
I carry a tiny gun CCW (Kel Tec P32) and a tiny light in my pocket - a Fenix or Ultrafire or other single cell cree light.
At home, I keep a full size .45 1911 (and other large guns...too large to carry concealed) and an assortment of flashlights handy.
If I ever heard an intruder in my house (has never happened, thankfully), I believe the light I would go for first would be the largest one i keep nearby....a 3 D cell Mag.
I've talked about this on several gun boards. Also, I have questioned the usefullness of night sights for self defense. In all the years, I have never heard one single argument that I felt justified the use of night sights. Yet they are among the most popular extras sold to gun owners. To me, they serve no purpose at all (other than maybe at a shooting range) - I feel the same way about rail mounted lights and lasers for self defene.
Just my 2 cents. And of course proper lights for weapon rails are expensive. So for me, they are not only useless, but expensive to boot. Again....I see no reason for them in civilan use at all. But I'm open to hear other opinions
Maybe people buy them because they have a "cool factor"? But IMO a hand-held larger light is just a far superior asset if a light is needed.
I'll add one last comment. Any money spent on accessories like rail mounted lights, lasers, night sights, exotic ammunition, etc...would be FAR FAR more effectively spent on lessons in how to properly use a handgun in self defense. I'd guess that 99% of gun owners today have little or no training at all. They don't even know the most basic rules of safety. The gun shop five minutes from my home has 11 bullet holes in the walls and display cases to prove that there are too many people with no interest in even knowing how to safely handle a deadly weapon. All that is required of them is they have the money to buy a gun and no criminal record.
To get a driver's learners permit, you have to read a pamphlet and take a one minute quiz to prove you did read it. To buy a gun....nothing at all. Scary!
Peace,
D.