Another major issue not mentioned with non-retina displays is that you have to chose between a decent on-screen text size and pixel scaling.

For example, I use a a 4K 27" LG monitor. If I use native 4K resolution, the text is way too small. If I use 2:1 resolution, the text becomes too big and I lose real estate. I ended up with a scaled resolution with pixel approximation. I won't explain here why it may be a problem for some people, but it is.