I bought a laser for my 9mm Ruger for two reasons. First of all, as a HD gun, I thought that I might get better target acquisition, even if the intruder is less than 20 feet away. I don't know how much it will actually help with that, but that's what I was thinking at the time. Points here in this thread are well taken, and I agree that short range SD situations are point and shoot - it's all muscle memory.
However, the second reason is for training. That alone is justification, in my opinion. My Lasermax Micro cost a little over $100, but has taught me at least that much about how I'm holding the gun.
In a way, it's like the underwater camera I own for ice fishing. Most people consider it a waste of money (those would be the anglers who have never used one, and no way to judge whether it's worth it or not). I've learned a ton about fish behavior and how to present my lures for optimum effect. In addition, I can see what's down there - both the type and size of fish, but also bottom structure, weeds, rocks, etc.
The laser is similar in how it helps me connect what's going on at target end with what's going on in my hand.
I would call it worth the price tag for what I learned. Would I actually use it in a HD/SD situation? Meh, probably not.