I noticed strange welder behavior and it can be usefull in some cases.
I made simple fence. To keep control on gap between panels and some nice edge chamfer i had to slice geometry. Because glass has physical material and I receve visible slices when rendering (screen). Even if i delete internal faces of segments.
When I apply welder modifier RC has to be in mesh display mode. But if I turn off welder modifier (not delete it) RC rendering as welded. And I can keep different display modes ( as on screen )