If you're hitting it like most people then you're not getting much out of it. You need to learn sidestepping and hitting the bag, and throwing straight punches like you'd normally throw, and some hooks.

If it wasn't for that it's only be like a bicycle machine for the arms. In my opinion it's the least useful of the hitting bags. I still use it as a warm-up, or finisher after everthing else is done.