I will agree that law enforcement when on duty needs a light. Lights are basically an offensive tool in this context. They are also more than likely to be up against an adversary for which a parlor trick works. If you are in a situation where you are fairly certain your firepower and training far outpaces that of your adversary and 5+ people are following you through the door a light isn't a bad thing.
WMLs... Usually throws off the balance of the gun. If it doesn't have a pressure switch on the grip it is hard to turn it on off. If it does have a pressure switch you have to deal with the wires and the holster/snag complications. You also can't throw it or leave it in a location.
I was thinking about needing to get kids at the end of my post as that would be a case where a homeowner basically needs to become offensive. I'm not there yet personally, so I don't give it much though. I guess my nephews are screwed if they spend the night. I think If I was there I would change my current bedroom in my house so mine would be the first at the top of the stairs. I'm a big fan of stairs as choke points.
What is inadequate about the dollar store flash lights? I don't have one. I have... IDK, ten. They are all over my house. The switch is the only thing I can complain about. The contact switch on a more expensive light is quieter and more responsive. The maglite XL 50 is 30 times as expensive as the lights I use though. I would never be able to buy ten of them. I also like the 3 AAA battery holders in the cheap lights giving 4.5 volts. Easy to wire them to other things.