My definition is dressing a wheel with a step of say .005 between them. I have done this with my old underpowered 5 x 10. So instead of a single .010 cut, you cut 2 x .005 at the same time. It seems to put less heat into the work, and needed less power.
On occasions I used with the cylindrical grinder as well when needing to remove alot of stock in a short time.
I have tried it for a final cut, like a .002 and .0005. it was not as good as a full face .0005" would be. But as you know YMMV.