And I can see more going on at the same time. It's absolutely more efficient than a single screen for my complex development needs.
There's just so many workflows that are so much better with multiple displays, but you really just can't see it? I'm sorry, but you have a mediocre computing experience, and I know it, because I have a laptop and I know what using one screen is like vs. efficiently being able to see more data at the same time. I know all the tricks, I've been computing for 40+ years. I also know that hardware is cheap, and my time is not cheap, and more information being displayed definitely does increase my efficiency.
I was just developing a 3d model using OpenJSCAD with code in one window, and a view of the 3D model in 2 perspectives in 2 other windows. I write code, hit save, and see the 3d model update, and it's a very visual oriented thing, switching windows so I can see the result would remove my ability to see the updates happen, which informs me that the model is updated correctly. I also have a debugger window open and other windows that I always need to see all the time. You just can't do this with a single screen, it's not possible without cutting the screen up into tiny sections or constantly flipping between them which is DX friction. It's simply an excruciatingly cramped experience to get what I have within a single screen, and no mental gymnastics you could do would change that.