It depends on what's being done/shown of course, if the phone is just logging the gps data and showing basic information such as elapsed time, speed, distance etc then the comparison to google navigation isn't really relevant.
Obviously if you've got a full map/tracking setup on the screen then battery usage is going to be far far higher, although far smaller screen + transflective + more power efficient soc might reduce the effect. Would be nice with things like Strava segments, but it's also on your wrist so not like you'll be looking at it that often when cycling.
For cycling I don't see the appeal of built in GPS, personally I've got a saddle bag that comfortably fits my phone so why wouldn't I take it. For those weird runners though I can imagine having a fairly bulky phone is a pain, they should get a bike
Obviously if you've got a full map/tracking setup on the screen then battery usage is going to be far far higher, although far smaller screen + transflective + more power efficient soc might reduce the effect. Would be nice with things like Strava segments, but it's also on your wrist so not like you'll be looking at it that often when cycling.
For cycling I don't see the appeal of built in GPS, personally I've got a saddle bag that comfortably fits my phone so why wouldn't I take it. For those weird runners though I can imagine having a fairly bulky phone is a pain, they should get a bike