Just move against a wall when jumping or falling and you'll notice all kinds of problems. Z to jump.
1) Player doesn't jump as quickly nor as high when moving against a wall.
2) Jumping and then moving against a wall sometimes forces the player to fall as soon as it reaches the top.
3) Move against a wall when you start falling and the player instantly reaches maximum falling speed.
*Preventing the player from moving left or right using "Is By Wall" helps but doesn't fully eliminate the problems.