Because Max's viewport instancing system only supports 1 mapping override at a time....so to avoid "why aren't my mapping overrides working" questions (for scenes with multi-channel overrides), I have instancing disabled if mapping overrides are applied by default, so users can at least see their overrides, even if things run slower due to no instancing.
If the Max devs eventually allow multiple mapping overrides per instance, then I would switch that to the default.
If the Max devs eventually allow multiple mapping overrides per instance, then I would switch that to the default.