I think the best part about LTE on the watch is that you don't know when you're using your iPhone connection or using the watch's LTE. It's seamless. If you're using Airbuds (which are a virtual necessity to get full utility / enjoyment from the watch), you can be making calls, getting texts etc. etc. and the proximity of your phone is irrelevant.
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Going phone-less isn't really an option due to battery constraints. My S3 will go at least two days between charges when mostly being connected to my iPhone, but you burn the battery pretty quickly if you're streaming music or making calls on the watch's LTE.
However, I decided to get a watch and airbuds instead of updating my 6S, and it was definitely the right choice (once I'd had Apple replace the phone's battery to end throttling).