It really depends on the task.
For writing and programming I also prefer a single monitor. I don’t mind switching from code to browser manually, and with 1080p/4K there’s enough space if you want to see both at the same time.
But for audiovisual production having a few monitors to extend your timeline or seeing a video preview at full size is really helpful. If you are retouching photos or working on an illustration it’s also nice to have a different view at a different zoom in a secondary monitor.