The serverside motion also moves the player every tick, however within the same game tick after being moved by serverside motion, the position of the player is reset to the position he was in before he was moved by the serverside motion. Therefore most players wont notice their serverside motion. However the player will have enough time (with time being a 0 tick / update order -notion) to activate pressure plates or tripwire, get damaged by cactus or lava, or pick up items in the position he was temporarily moved in by the serverside motion.