Drywall, gypsum, sheet rock, wall board, or whatever you call it, has to be installed by someone, so who better than a drywall installer? Some drywallers install the board and also tape and mud the joints, but others only hang the board.  

When sanding, drywallers are exposed to a lot of dust, including silica in some cases, which they need to be protected from.  The Center for Disease Control suggests using a vaccuum sander or pole sanding to reduce worker's exposure to harmful dust particles