Without defending some of the atrocious behaviour I've witnessed, I think it's fair to say that a certain amount of throwing would make the job quicker and easier.
Use the lifting action to impart some horizontal momentum, provide a bit of guidance as to direction, let go and move on to the next bag. The alternative, is pick up, support the weight until at destination, then put down.
The critical thing is that whilst your bag is "flying" through the air, it's not really having to be supported, so the handler doesn't have to be as correctly positioned. Anyone travelling with a heavy bag does the same thing at check-in. They can heft the bag on to the scales without too much difficulty but it's not so easy to reach over and lift it back!