To be honest, I'm not too sure what the slide was meant for either. The lead developer told me to add crouching sprites and I programmed in the crouch, then he later told me to add sliding sprites, so I replaced the crouching sprites with sliding sprites. The crouching sprites end up going unused for this reason. Maybe he had plans for later on that weren't communicated, but I didn't have any ideas for the slide either, so it's kinda just left in as an unfinished mechanic.