I've got a quality laser on my .22
Its great for low light when you are struggling to see properly through the scope, it is very good for shooting from the hip or really close range stuff.
You can get accurate shots off really fast because you don't need to find the scope, get a proper stance and hold.
Don't buy a cheep one, I'd recommend a Laserex like this one
http://www.ssaa.org.au/industry-news/20 ... sight.html That's what I bought from my LGS many years back and its still going great.