Enable running, so you can get a good running start before jumping (ctrl+r). While running, press jump, but then release the jump and "forward" key immediately after jumping. Compare this to when the forward key is held, or when another key (such as "back") is pressed while in mid-jump. Perform the same test on the main grid. You should see a huge difference in the inertia while jumping. This causes slam-dunking in basketball to be possible only if you jump while standing very close to the rim. I am sure there are other implications as well. On the main grid, you maintain some inertia once you have started jumping, which enables you to release "forward" or even press other directional keys without dropping like a rock.