I have had some fun playing with nav apps, taking pictures, and recording my track with my I-phone. Whenever someone wants to know exactly where we are I show them the Gaia map on my phone.
However, there are a few advantages of taking pictures with my little Lumix camera (more pixels, more zoom for example). I also am an ardent supporter of carrying a paper map and compass in spite of the phone map and compass because the batteries in the phone don't last forever, especially with two GPS apps running.

So I am considering leaving the phone at home or well-hidden in the car when I hike. I liked the Under Armour app and all the data it reports (distance and elevation gain and pace for example), but those can also be easily calculated.
Do you carry a phone with nav. apps? Why or why not?