Weapon-mounted lights (lasers, IR, etc) can be considered from the perspectives of equipment, envisioned circumstances and training needs.
Just attaching one to your favorite firearm doesn't mean you know
when, why or how to use it safely, appropriately and effectively in any particular situation.
Then, there's making sure it's the correct make/model for your firearm, and that your firearm continues to function normally when the light is attached, and that light remains properly attached during continued use. (Our armorer bench at the agency range had a little pile of parts which broken off, or had to be removed from, guns that were in-service. Maintenance and repair of equipment is an important consideration.)
Some training and familiarity with the safe and proper operation of equipment is always prudent, as well as considering how user operation may be affected by stress and dynamic situations.
http://www.denverpost.com/news/ci_25921024/gun-mounted-flashlights-linked-accidental-shootings
Buying a guitar and learning a couple of chords, only practiced every great once in a while, doesn't guarantee skilled musicianship. Trying to play those chords without mistake when being watched by strangers? Well, even mild personal stress can introduce some unexpected difficulties not experienced when quietly practicing alone.
Look at how people make mistakes when driving their motor vehicles, and that's something many people get the opportunity to do every day (unlike using/practicing with weapon-mounted lights and the firearms to which they're attached). Throw in some unexpected circumstances and a little stress, and people can fail to react properly and get involved in, or cause, accidents.
Handling and using a weapon-mounted light involves handling the weapon to which it's attached, at the very least, and that introduces the potential to mishandle things and make unintentional errors in manipulation. Kind of like how 2 of the most dangerous times involving manipulation of firearms is when loading and unloading them.
I usually suggest someone consider getting some training in the safe handling, operation and use of equipment, including firearms and anything attached to them, like weapon lights.
Just my thoughts.