The default WalkSpeed for ROBLOX characters is 16 studs/every 10 seconds. A higher number equals a higher speed, and a lower number equals a lower speed. Before an update, if WalkSpeed was negative, controls would be reversed. Now, you wouldn't be able to move at all. If WalkSpeed is high enough, a player can run through walls depending on how thick they are (i.e. having a speed of 250 might make you pass through a 1-stud-thick wall).