I agree and disagree with both sides. One thing that someone pointed out is that it doesn't hurt to have two lights. one in your hand, and one on the gun. You don't HAVE to use the one on the gun but it's nice to have it just in case.
the way my house is laid out it's like a "V" my master bedroom is at the bottom of that "V" so anyone that might have come in through a bedroom window will need to come down the hallway from the right, and anyone from the living area will come from the left.
Sitting in the bedroom, behind the bed, on the phone with 911 will allow me a perfect view of the door to the master bedroom. I also keep at least one or two lights on in the house even at night. small lights, but enough that I can easily see at night. I have a revolver and a LED maglite in my nightstand. I also have the benefit of having hurricane windows. Ask anyone in Florida, the chances of someone breaking in through those is VERY slim. Fire departments don't like them because even they can't get into a house through them without some extreme measures.
In the living room I have a PX4 with a streamlight on it as the patio on the back of the house is off that room and the backyard is not very well lit. yet. We live on a lake so in case something comes up out there I have, again, both a handheld and a gun light. If I did identify someone, regardless of what light, I could easily flip on the gun light, drop the handheld and use that hand to then dial 911. Now if I've only got a handheld light, how am I supposed to dial 911 while holding the gun and the flashlight? Or do I drop the gun to dial? do I drop the hand held flashlight so I'm now in the dark again?
And before anyone says it, no, I'm not calling 911 on every sound I hear in the backyard just for them to come out because of a big bad raccoon or opossum that wants to eat one of my tomatoes. haha.
Basically though, it's like having the gun itself. Just because you have it, doesn't mean you have to use it. But in that one scenario that you do need it, it's damn nice to have.