VERY VERY VERY IMPORTANT!! I removed my popcorn ceilings and did 3 layers of mud to get a smooth ceiling and the dust was horrendous. I'd close off a room with plastic to try and minimize the impact. I didn't want to be breathing in that dust where I was sleeping, so I cleaned after each round of sanding. I hired out drywall work and the contractor was very good at cleaning the work area everyday, which I very much appreciated.