I make sanding sugar cut out cookies often. I sometimes have excess sugar left on the cookie sheets after baking. Could this excess sugar be saved and reused for the next tray. I often dump the excess in the trash and feel like I am wasting it. Any answers would be appreciated :)
The main issue with reusing the sanding sugar is what else may have been mixed in to it:
Within a single baking session, I would certainly reuse the sugar.
It would be a more significant issue if you are retaining the sugar between sessions, but still, unless there is dough with raw eggs mixed in with the recovered sugar (which would no doubt be a very tiny amount, and soon quite dried out), neither of these is a safety issue, although they may be an aesthetic issue.
I would ask, though.. how much extra sanding sugar are you loosing? If you sprinkle each cookie (rather than casting sugar across the entire sheet) you should have very little excess sugar to recover.
Still: reuse it if you want to, and you are not displeased by its performance when being reused.