It gives a small boost of speed without any animation.
Edit: I figured I should explain why this bug is problematic; It's very anti-synergetic with sneaking.

If I remember correctly, holding shift (with default controls) would sneak, while tapping it would use a movement skill in the last update. Right now the skills are used whether the button is held or not, so this may be two bugs relating to movement skills.

Fixed in 18.3.1