What is the benefit of a "riser leg, fast fit, easy fit" shower tray legs?

The riser legs can be fitted to the underside of the tray and allows the installer to raise the tray off the floor.

This is useful when installing the tray on a solid floor, where the shower waste cannot be buried into the floor. Accurate adjustments can then be made by raising or lowering each leg to obtain a perfectly level tray.