I think generally speaking, you know when you're going to want to take a photo, or be navigated via gps, or listen to music. So why not take the route

I think generally speaking, you know when you're going to want to take a photo, or be navigated via gps, or listen to music. So why not take the route that allows you to experience those tasks at their best? Because life is all about trade-offs. Yes, I can buy an eTrex, a Nikon D5, a standalone audio player, and a phone. But now I have 4 devices, each of which needs to be kept charged and kept track of. With a smartphone, I have a decent GPS, a decent camera, a decent audio player (which can play FLAC with the right apps), and a decent phone. I can carry one thing in my pocket, or a backpack full of gear. That's not to say there isn't a time and a place for specialized kit. If I'm camping, for example, I'm definitely going to use a dedicated GPS device, rather than an easily breakable, low-endurance smartphone. If I'm out on vacation, I'm going to take a proper camera in addition to my smartphone. Most of the time, though, I don't need the advanced capabilities that a dedicated device would give me. A phone gives me easily 60 to 75% of the same capabilities, at a much smaller fraction of the space needed.