I used to believe this but not anymore. Way back in 2007, I spent $2500 for 2 Samsung 30" 2560x1600 monitors ($1250 each). I envisioned a massive productivity increase with scenarios such as:
- email inbox one screen with main "task" window on another screen
- video tutorial (e.g. Photoshop training) on one screen while following along on Photoshop on the main screen
- debugger on one window with the code output on another screen
Eliminating all the Alt-Tab window switching would be supposedly be gone. That was the theory. The problem is that I didn't realize that my eyes hated having these giant lightbulbs in my peripheral vision. It was uncomfortable enough that I often powered off 1 monitor which negated the point of multiple monitors. The other thing I didn't like was the extra heat 2 monitors would add to the room.
I went back to 1 monitor and Alt-Tab is minimized if the single monitor is big enough (at least 27") to have multiple windows of reasonable size. For me to go back to multiple monitors, I'd need the "wing" screens to be color e-ink panels[0] so that they don't act as bright flashlights in my peripheral vision.
I recognize the productivity benefits of multiple monitors -- especially for "dashboard" and monitoring[1] such as stock trading, devops IT corporate/cloud systems monitoring, SpaceX rocket launch monitoring, etc. Having your peripheral vision notice an abnormal activity is useful in those scenarios.
[0] https://www.google.com/search?q=e-ink+panel+&tbm=isch
[1] https://www.google.com/search?q=multiple+monitors+trading&tb...