Same here. Only my long runs are on rough trails. Falls happen. My watch is cheap and welcome insurance.
Real world answer: People who run long distances and don't want to carry their (increasingly larger) smartphones with them, but must have a method of communication with them for safety reasons.
For example, I run multiple marathons a year and am training year round. I go on long runs all the time. I also live in the middle of a very large non-pedestrian-focused city with a lot of drivers who are generally oblivious to pedestrians, and have had several close calls over the years. Additionally, I'm an asthmatic and while problems are rare–there's always the threat of something bad happening. I have to have a way to call in case of an emergency. For people like me having a watch that can do emergency calls (or allow you to receive messages while you're on a 3+ hour run just in case someone else is having an emergency worth cutting your run short for) without having to carry a large device with you is very appealing.
Edit: Clearly this isn't a need that isn't covered by a phone. It is, however, a substantial quality of life improvement for some.
Sadly, I don't think this is a realistic use of the Apple Watch. Real world facts...
1. Zac Hall of 9 to 5 mac just recently ran a
half-marathon (13.1 miles) only using the AW3 and AirPods. He used LTE music for streaming (as well as some music downloaded on the device) plus some text messages but didn't make a call. He left GPS and optical HR on. Both the AW3 and AirPods were at 100% to start the race. He finished in about 2 hr 30 minutes and had 2% on his AirPods (he believes they didn't last the 5 hour rated life because of the high volume level he used) and had
13% left on his AW3. You could obviously save battery life by turning off optical HR and GPS (but I don't know marathon / half-marathon runners who would want or be willing to do so) or avoid streaming music with LTE (but then you either have to slowly download music to the watch in advance or run without music and not many runners would be willing to do that either.)
2. Because of this level of battery performance (consider again he made NO voice calls) it is IMHO unrealistic to do more than a 1 hour away from the iPhone workout using LTE streaming without needing to immediately charge the AW3 to get through the rest of the day. For *many* I understand 1 hour is likely to be enough but not someone "running multiple marathons a year". You would need more, certainly to get through the day but also the workout itself. I doubt a marathon runner could get through even longer training runs let alone the marathon if you used LTE+GPS+HR at the same time, and that is without even needing to make a voice call in an emergency or otherwise.
I think future models of the AW will clearly "get there" in terms of battery life and it may be there for most of us already, but the dreams of taking your watch for your 16-22 mile training run while streaming music (or a podcast, whoops can't do that!), tracking GPS, tracking your heart rate, having an emergency reserve for a brief phone call or two AND then hoping to not have to recharge to get through the day is simply that right now, a dream.