Imagine that you are doing multi-tasks: chatting with Yahoo Messenger, watching video with Media Player, surfing with Firefox, typing report with MS Word, programing with Crimson Editor, analyzing results with Matlab and Tecplot... It's difficult to display these applications on a single monitor.
Luckily I have a temporary LCD, and I can use the "Multiple monitors" function to display them to two different monitors. That's really easy and the result is great.
Try this:

• connect 2nd monitor to your laptop,
• right click,
• choose Properties,
• choose Settings,
• click number 2 on screen,
• choose screen resolution,
• stick "Extend my Windows desktop...",
• OK

and you will see the magic.