This means the 27” 4K monitors that are the industry standard now for some reason at 3,840 x 2,160 are almost twice the size, yet have barely more resolution than the MacBook true retina screen.

MacOS can do scaling to adjust for this, but it uses the least amount of resources in native or pixel doubled mode. Any display that is between the resolutions I mentioned (like 27 4K) requires fractional scaling.

This is more resource intensive, and doesn’t look as good as pure retina.

Here’s a better explanation: https://bjango.com/articles/macexternaldisplays/