My main goal of using SAMs is to avoid base attacks and to down UFOs so I don't have to bother with sending out interceptors.
So for my main base in Europe (covering Europe and parts of Russia, Middle East, Africa) I plonked down a workshop base and a hangar base right next to it, all with a couple of missile bases, and SAMs around them. Nothing ever gets through (until the aliens attacked by land).
I have also found that missile bases are more useful in bases than laser bases, just because of their greater range. Laser range is so small that you usually only ever use it in the case of a direct attack, while with lots of missiles you can often cover a nice area as well.