: I don't know why anyone would use a variable speed ROS as the whole idea of that sander was to eliminate the swirl marks and it was done by most models by increasing speed, and using multiple orbits. Decreasing speed can only work to
eliminate one of the advantages of the ROS.

The one case I've found for reducing speed is when using coarse paper on the initial rough sanding. Cedar can sure disappear quickly! On my Bosch DVS I got great results using 40 grit but backing off on the speed a little to control material removal. Also, when sanding between hardened coats of epoxy your goal isn't always a complete absence of "swirl." The ability to slow the sander gave me the ability to control rate of removal of the hardened epoxy. That way I could hit the runs, etc. and not worry quite so much about the possibility of suddenly seeing daylight where it shouldn't be. Maybe it was "all in me head!"