In reply to bigbobbyking:
> And better battery life. If you try and use your phone for long periods of GPS tracking it will kill the battery. Especially in cold conditions and if you keep taking it out to look at the screen.
This. A phone is far more fragile than a GPS watch, and is running so much other stuff in the background that even though it has a larger battery the battery drain with GPS is rapid. Not sure if it's something to do with the surface area for heat loss from a phone battery being large, they also drain frighteningly quickly in sub zero temperatures. Also it's no fun opening up an app on a touch screen in the rain.
Don't get me wrong, I used to use downloaded maps on a phone a lot (with a paper map as and a compass as back up). Since I've been running a bit more I've started to go back to a photocopy of a map and a thumb compass in one hand, and a quick check at OS Grid Ref and elevation on my watch as a cross check of my nav. Also concentrating on pace counting for distance etc stops me worrying about all my aches and niggles.