What does satining your yo-yo mean?
-yoyoingmonkey
Sanding it down to make for better grinding or just to take anodize/ paint off.
Yeah that is pretty much it,
also I redid the title 
It creates little trenches where you sand- due to the roughness of the paper, will help your grinding by removing some of the friction. (Little trenches=less yoyo grinding on you=WIN!)