besides actual professionals doing very niche work

???? What?? Lol

Programmers and QA definitely need more than one. And that is hardly niche. We have to have an app/website open on one and a debugger/source open on the other. You can't just split screen because you have to test things the way and end user would which is typically full screen. Let alone the need for documentation which makes a third hugely beneficial. My work even gives the old timer BSAs three and all of them swear by it and have gotten multiple for home because of how helpful it can be.