The main function is to use it as a free-standing bag. Because the most of the weight is at the bottom, the bag gives you great feedback after punching or kicking. Also if you punch and kick is strong and you put the bag down you can use only one finger to put it back to the upright position.
When you are tired of running around the bag and practicing stand up techniques - take out of the base and start something completely new. With no base the bag stands itself so you can easily have it ready for practicing take downs, throwing or ground & pound.
When you miss the classical heavy bag, all you have to do is unpack the straps, hang the bag and you can star practicing. The bag is not as heavy as the regular one but because of the weight on the bottom it still gives you excellent workout.