1)Ammo is cheap and readily available anywhere
2)You don't have be an expert marksman to hit what you point it at (it's called a "scattergun" for a reason)
3)If you choose to, you can go for a disabling shot and have a reasonable chance of actually hitting a leg, arm, etc.
4)Also If you choose to, it can be quite lethal (though maybe a little messy)
5)If you have neighbors like I do, you worry about penetration. Steel shot probably won't penetrate your wall AND your neighbor's
6)Deterrance: The sound of a shell being jacked into a pump shotgun's chamber has to be the scariest and most distinctive sound in the universe.
Enough to put most burglars to flight without firing a shot.
A friend of mine did that and got the satisfaction of watching a would-be burglar void his bladder.