I have always carried a handheld light, all the time, even during the daylight hours. However, I have never carried a WML (Weapon Mounted Light) on my carry handgun. I have always, though, had a WML on my dedicated house gun and that has been the case since handgun sized WMLs first became viable.
The use of white light to aid in shooting in darkness is almost non-existent in civilian self-defense, despite the fact that there is a big training industry dedicated to “night fighting.” The reality is that criminals conduct most activity during times of “low light,” but they can’t operate in “no light.” Most criminal predation happens under streetlights in parking lots where there is enough ambient light for the criminal to see his intended prey, and enough light for the intended victim to shoot the criminal in the face without the need for a light.
Even though the use of a flashlight with the handgun is all but unheard of in the real world among civilian self-defense, carrying a bright handheld light is a must. The light is necessary for lighting up dark places that may hide dangers, and the light can be used to intercept and identify approaching strangers in the night. Only a handheld light is appropriate for those tasks, not a weapon mounted light.
In the home, however, having a light mounted to the handgun makes sense as it is possible that you will only have the single object in hand when responding to a home invasion. Further, being able to use the light with the gun, all with a single hand, may be needed in home defense. For these reasons I believe in the utility of a WML on a dedicated home defense handgun.
See the video for a further discussion on the usefulness of a WML in this capacity: