It's a cheap small device that's extremely portable. When I was doing more random tech support things, I'd probably try to keep one in the backpack because it's relatively tiny. It can handle boot media, pxe, testing random hardware, connecting to networks you need, etc. It would come useful when I don't have a laptop / didn't expect to need to do work, but it turns out I'd really like my laptop right now. At that size, I'd just never take it out / leave behind.

Although with the new, more powerful phones I could also carry a small USB dock instead. I've done random emergency work on N900 before.