I'm not the OP, but I assume hi-DPI support means that applications scale up their GUI sizes appropriately based on the DPI.
When I use a hi-DPI display (like 4K displays), a lot of old software renders text and widgets too small to see, because they were programmed to display things as so-many pixels high, without concern for DPI. It's frequently a problem with old video games, though it affects regular applications too.
What difference does it make if the standard resolution is Hi-DPI or not? Can you visually tell the difference between pixel doubling and other methods of designing for Hi-DPI?
When I use a hi-DPI display (like 4K displays), a lot of old software renders text and widgets too small to see, because they were programmed to display things as so-many pixels high, without concern for DPI. It's frequently a problem with old video games, though it affects regular applications too.