This is the mouse I use when I travel with my laptop. First off, it's wireless; you just plug the receiver into a USB port on your computer, and you're done, without installing any software. The fact that it's wireless makes it great when working on the train, for instance, or even just when you're not sitting at a desk with it. It works on almost any surface, including my sofa arms and even my legs!
Secondly, it's a really good, compact size, which again makes it perfect for travel. Rather than bundle a big mouse with wires trailing into your laptop bag, this just slips away.
Thirdly, for its size, it's nice and robust. The buttons feel solid when you click them, and the wheel has just the right amount of give.
But yes, there are also disadvantages. Like, for example, the fact that you have to sacrifice one of your USB ports. You'd also have to if you were using a wired mouse, I know, but if you normally use a touchpad, this is one sacrifice. The other, of course, is the fact that it's battery powered. Which means that you'll need to either buy batteries for it, or recharge them when they're out of juice. And, for a product which prides itself on its simplicity and mobility, this kind of defeats the object.
Overall, however, these disadvantages don't really matter: Like I said, you'd still be using a USB port with a standard wired mouse, and the battery life is generally rather good. Just remember to turn it off when it's not in use, and it should last for a few months.