In this clip you can clearly see the screen driving the water toward the centre of the screen, such is the strength of the screen's diffussing effect on the water flow into the brew chamber

The natural path of water on a lever group machine is to jet down the bore of the sleeve and exit around the perimeter of the shower screen, and you can see that this screen addresses that very effectively

The result for you is exceptional espresso more often; it improves consistency by reducing the chance of washout on the top of the puck, preventing channeling from getting started because of the softened entry of the water into the brew chamber