The exercise improves bench press technique and horizontal pressing mechanics. Here are several of my clients, including NFL athletes Jarius Wynn, Michael Montero, and Jake Banta, demonstrating a few variations:
As a result, the stimulus to their chest, shoulders, and triceps is minimal. Using the leg raise during chest presses resolves this. It helps to isolate the upper body by eliminating the assistance of the legs. This is also the grand equalizer of all bench press protocols as it's a true indication of upper body strength.
Both methods involve a straight-leg, ankle-dorsiflexion position: