Horizontal is directly in front of me, used for whatever I’m currently focusing on - usually IDE or browser.
Vertical is to the side, used for anything auxiliary to my current task - browser, bug report, notes, chat, git gui, etc.
Laptop monitor is for anything I want to monitor, but don’t need to look at constantly - logs, news, incoming bug reports, etc.
I also make use of virtual desktops, so I have one for chat/email/general browsing, one for code editing with browser, git gui, IDE, and one for notes/zoom. Laptop screen doesn’t shift with virtual desktops so I always keep the monitoring open.