I think this setting might only be useful if you have "Prevent Loops" set as a route control,
(I've had trouble placing extra vias with the "prevent loops" setting turned ON),
Also, in your DRC check, the extra via won't be flagged as a "hanger"
I suspect this is an old setting that is not very useful anymore,
now that we can do things like multiple thermal via grids buried into power pads, for example
Jack