Does anyone have a dual-monitor setup, if so why and how often do you use it? How useful is it?

I've just bought a large 22" monitor for my office so I can do more work there, to plug into my Laptop (there is no desktop or anything else up there previously) and now am using my Laptop monitor as a second monitor. Finding it useful, working on the proper monitor, with background info (realtime stats on how all my businesses are doing) displayed on the Laptop. Almost makes me tempted to get a second monitor for my Desktop at home but not sure its worth it or not. The background info I've got running on the Laptop I normally have running on my iPhone when at home already anyway.