This has been on my mind lately and I'm curious how my perspective on this compares to the thoughts of others.
I always wear a respirator when spraying anything, but when sanding, I almost never do.
When I sand by hand, I figure I'm not raising that much dust, so I don't normally wear a mask.
When I sand with my Random Orbit Sander, I connect it to a vacuum which does a surprisingly good job of removing the dust through the 5 holes in the sanding disk, so I don't wear a mask. In addition, I think the dust removal from connecting the ROS to the vacuum makes it sand more effectively.
Curious for thoughts from others.