Very interesting conversation.
...and handling a light that's not mounted is just not feasible with a long gun.
I'll begin by disagreeing on this point and tie it into another in a moment.
Firstly;
I have a light mount and light with momentary pressure switch, both made by Coast Products, and a magazine tube clamp made by CDM Gear. I have all this on the 20" Persuader mounted on the support side. Typically all this is actually on the gun, but we have chickens and sometimes hatch eggs and the Coast light is the best I have so it gets used to candle eggs. It hasn't been on the gun in awhile.
Here's the relevant part. I had a critter bothering my chickens a couple months ago. I grabbed the gun and light and headed out the door loading buckshot as I went. I turned the light on and held it between my index and middle finger of my left hand and was able to use my thumb and index finger on the forend.
(You'd be surprised the added flexibility of movement this allows to scan an area)
Gentlemen...I beg to differ...
Shotguns are not point and shoot weapons...and are capable of great accuracy with any load when aimed precisely, especially at distance.
Here's where I dovetail the story and make a second point;
As for aiming, I keep a Meprolight tritium bead on my gun. No point in having an HD/property gun which may be needed at night if you can't see the bead.
Back to the story,
I'm outside, gun shouldered, light on and scanning the property. I pick up a low set of eyes in the light. We have all the usual suspects out here, any of which will make off with a chicken. I move that tritium bead to the eyes and shoot the target which was about 35 yards or so and I dropped it where it stood. ("accuracy with any load when aimed precisely") just as
@SHOOTER13 mentions above.
Moral of the story;
If its to be used at night, yes I believe a light is almost entirely necessary.
At typical HD/SD distances, nearly every load is a precise load, even smaller shot (which I would not use defensively). Only a few loads fall apart and spread over very little range with Winchester SuperX being the worst in that area in my experience with a widening discernible pattern after just 7 yards.
Now I don't believe that when folks here say the shotgun is point and shoot they're implying aiming isn't necessary. I believe that in and HD scenario, say 7 yards or less, if you put the bead on a target, it will be hit, (unless your angle is extremely weird, almost humanly impossible), but certainly you won't get patterns that spread and put a pellet in every square inch of wall space. The load will in fact, in most cases, make a single hole.
A laser for a shotgun... I dunno, I've not ever tried it. My concern is that point of aim and point of impact will be two different thing. Not to say it can't be used as an aid as has been mentioned say if shooting off hand or in a situation where conventional sighting just isn't an option.
Gadgetry though isn't a surrogate for practice, so whatever you go with, just get plenty of ammo and of different makes and models and shoot at varying distances to help you determine what will suit your unique needs.