Cutting parts on tools like a band saw can leave you with a rough edge, and depending on how good of a saw user you are, you might still be need to remove material to get to your designed part shape. Disk sanders are helpful to sand off rough edges and get your models in good shape (literally!). Using a disk sander is much faster than sanding by hand, so it's helpful to know how to use one safely so you can speed up your workflow.
Holding your parts up in the air and approaching the disk can be unsafe. You have way more control if you place your part on the bed and then move it up to the sanding disk.
Since the whole disk is spinning at the same rotational speed, that means the surface speed of the disk is faster towards the outer edge of the disk, and slower towards the center. Use the outside edge of the disk to remove more material, and the inside to remove material at a slower rate. Remember: keep your part moving to avoid building up heat and potentially burning your part (or the sanding disk!).
Always use the brake to bring the disk to a complete stop after you are finished using the disk sander. This is particularly important for student spaces because they tend to be crowded, so it is important to avoid situations where someone could get hurt by being near a disk they were not expecting to be moving.