1 screen is not enough for me anyway
Keeping client details open in one window and answering a support ticket in another is very handy. Also, if you are doing comparison of codes, monitoring servers, running multiple shell commands (ever run TOP and MyTOP and mtr and then need another shell screen to execute commands?), it's a wonderful thing
Primarily I have multiple chat windows open with customers and shell windows open to help resolve their issues. Flipping back and fort with multiple desktops doesn't quite cut it. It's like using two notepads rather than flipping pages and losing your spot. It's multi-tasking at it's best.