I have three 27" screens (iMac in the center and two thunderbolt displays on each side) and I use most of my "daily driver" applications fullscreen (single monitor). So, things like Xcode, VSCode, web browsers, mail, Quicken, Spreadsheets and Word Processing, and so on. This gives me usually at most 3 things to do at once. Occasionally, for smaller apps, like calculator, messages and so on, I won't fullscreen them. But for my main workflows, it's fullscreen all the way.

My actual biggest pet peeve with this setup is the vast number of web sites that deliberately choose to limit their content to a tiny column centered horizontally in my browser, with 10cm of wasted whitespace on each side.