The bigger issue, for me, is using two monitors with different resolutions. To get a usable font and UI size on a, for example, 4k monitor, you have to scale it up using xrandr. This, however, also scales up the lower resolution monitor, so now its font and UI size is too large. If you try to scale that monitor down you will be very disappointed. This is because X11 treats the "monitor" space as one continuous screen, meaning that scaling the lower resolution monitor down also moves the screen that is supposed to be on the higher resolution monitor into the lower resolution monitor.