When I go travelling I carry quite a few gadgets with me. My Pocket PC phone, the Creative Zen Vision, Bluetooth GPS unit and a Nintendo DS Lite.
Some people wonder why I just don't get a powerful, GPS capable Pocket PC phone and thus elminate the need to carry around so many other doodads. Well there's a simple answer to that question.
Battery Life, the phone when in use has about 3~4 hours of continous ON time, meaning backlight on and I'm doing something with it. Like a notebook the actual time depends on what I do with it. The Zen Vision also lasts about the same time, the GPS lasts about 10 hours, but I never tested it before. And the DS Lite lasts about 5 hours.
Now... if I only used the Pocket PC for all my entertainment purposes, within 3 hours I'd be without a phone. Which is definetly not a situation anyone wants to be in. But with seperate devices I don't have to worry about the dependencies on one battery, I can keep watching movies on my Vision till the batteries run out, play my DS lite till it goes flat and still my phone has enough juice to get through the day.