Lets you disable the rotation of the floating UI menu so that it appears more like a flat surface, no matter how your hands are tilted or whether you look up and down, see the attached video to see what it does, as it is difficult to explain.

You can enable or disable the restriction of the UI menu in the Session Plugins menu "No VR Hud Rotation":

• Disable Rotation: Tilt: the UI menu does not lean left or right when you rotate your wrist to the left and right
  
• Disable Rotation: Horizontal: Recommended to leave off. The UI menu does not move / rotate left or right around your current position in VR space
  
• Disable Rotation: Vertical: when you look up or down, the UI menu will not "look down" on you, but will remain a flat surface, parallel to your upright standing position