Re: The main reason for wearing a watch
I'd disagree to an extent, based on my own experience.
When I first started running I used my phone, as I had it, and didn't want to splash out on expensive kit for a hobby I might not keep up. However, to carry it you need either an armband (I sweat a lot when running, so uncomfortable for me) or a suitable pocket. That lead me to start buying Ronhill shorts, which although great, aren't cheap, purely for the large pockets at the rear waistband. Even at that, the phone is still heavy and moves around a bit.
I have 2 watches, a normal one for everyday use, and a TomTom runner 2 cardio + music that was a gift for exercise use. I like to listen to music when I run, and it's lighter and more convenient than my phone, and you can disable all the trackers so as not to turn in to one of those irritating toolbags who feel the need to tell everyone how many steps they've done that day.
Shame TomTom have exited the wearables market though.