Function: turn sideways without losing speed
The cross-steps rotate your body from facing forward, like a sprinter, to facing sideways, like a thrower, over roughly 3 to 5 steps, and they need to do it without bleeding off the horizontal speed you built in the run-up. This is the single hardest coordination task in the throw, which is exactly why most programs drill it in isolation rather than only inside full throws. Get it wrong and even a strong arm cannot save the distance you already lost in the turn.

