Air Rifles are awesome. There are plenty of reasons why I feel this way. I love the idea of a rifle that I can shoot without having to stalk ammo, and then pay exorbitant rates too!
Shooting at home
I have a couple Daisy air rifles, these are prefect for plinking in the backyard (provided you have an adequate backstop). My kids can shoot soda cans all day long for pennies in ammo. I Used to be able to drive out to the desert with my kids with 22 rifles, but with ammo costs, those days are much more rare. This way we can shoot anytime from the comfort of home.
Nice and quiet
Air rifles are nice and quiet. I love not having to wear hearing protection when shooting, and I am not giving away my location to everyone within at least a mile radius either.
Air rifles are cheap to shoot, but you can also own a high quality rifle for a fraction of the price of a firearm. Backyard plinking guns can start at $29 at your local big box store, and you can get rifles capable of muzzle velocities up to 1000 fps for around $99.