I have two 4k monitors, and two laptops and a desktop controlled from one mouse and keyboard with seamless traversal across all of them thanks to mouse without borders. Desktop goes to one 4k monitor, split into 4 quarters to give the equivalent of 4 1080p screens, and each laptop is displayed side-by-side on the other monitor (plus their own 1080p screens to give 3x 1080p screens equivalent each... The picture in picture mode on these lg's is actually usable). It's an upgrade from the previous 4x 1080p screens to the equivalent of 10x 1080p screens, and I still need more screen space!
Coding, system monitoring (Work / Home network), Slack / Meet / whatever... generally I'll have 3 or 4x screens-worth doing work stuff, 1 or 2 for monitoring stuff, one or two for various chat sessions. It's easier than alt-tabbing all the time.