One of the surprises when we pulled up the rug in the office was the polka dots under where the plastic, anti-static desk floor  mat was. The mat had little protrusions to grip the rug. The rug was a normal thickness, large area rug. The mat was on top of that and our chair would roll around on it. Anyone considering those mats may want to put a thin plywood or something down underneath it.  Those  dots are dents right through the finish into the wood.
I’m not upset about it in this room as there are lots of other issues with the floor finish. But I thought I’d warn anyone else that may be using them.