Perform multiple functions on the same piece of brass while only handling that piece of brass once, i.e. decap, size, neck expand or seat then crimp. Also I can have multiple cartridges worth of dies setup at one time on the same turret. Considerably more efficient way to work vs placing and removing the brass for every desired step and setting up dies between every step.
I like completing the same task for all the brass before I start another task. Doesn’t seem like a big “time saver” for the extra cost.