Snow and mud tires are called "Winter tires" nowadays. They are made of a softer rubber (so as to provide better suppleness in cold temperatures), which is why they don't last as long as regular tires. That's the reason to put them on in November and to take them off in March or April (around here, anyway). At that rate, they will last 3-4 seasons.
Important safety considerations with winter tires: Always put them on all 4 wheels and never replace just one: replace all 4 at the same time.
But how do you know whether you need them? In my opinion, if you need them, you will know it - but here's a good piece on the subject.
With global cooling picking up its pace, everybody may need them soon. 4 WD is good but, where you need them, winter tires are as good or better.