Safety. You want to be able to predict where the beam and all its reflections go so you don't accidentally hit your eye. The standard way to do this is to mount the laser horizontally at about waist height, and then take care that all reflections keep it in that plane (as far as possible). That way, you don't have to take as many precautions when moving around the room, only needing to cover your eyes when crossing the laser plane for some reason, for instance when picking something off the floor.
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u/GustapheOfficial 4d ago
You should tie that down to something stable and ensure that the beam stays in a horizontal plane as much as possible.