I use three at the office, and two at home.
In both setups the laptop is my keyboard and small screen, above it is a 34 inch 21/9 aspect ratio curved display. At the office I also have a standard monitor off to the side.
The large screen is my primary work space, with various code editors, UI dev tools, web browser, reference docs, and terminal windows.
The laptop screen has email, all my short cuts, and a virtual version of the UI I'm working on because it is also a touch screen.
When I have the third screen I use it for teams, a few system monitoring tools, and youtube for music.
I used dual side by side monitors for years, but found that having the split in the center meant I was always sitting with my neck turned, and this lead to a lot of pain and headaches. Having them top / bottom is a lot more comfortable and my large screen is high enough I now sit up straight.
A curved screen at the right distance also means a lot less eye strain.