If you don't run an engine frequently the gas can go bad. The gas inside the carburetor can thicken and cause the small parts to get stuck and not move. A good way to tell if your fuel system is running good is to give the ATV a ride-test during your after-storage maintenance routine.
Knowing how to take apart a basic carb and put it back together can save you time and money. It can save you time because you can do it in just a couple of hours. It can save you money because you won't have to pay someone else to do the work for you.
Most single barrel carbs are fairly similar in design so this method should work on most engine/carburetor combos. You'll know you need to clean the carburetor if the gas smells like lacquer thinner or turpentine or some other non-gas funky chemical odor.