My girlfriend wants an Apple Watch, so she’s going to get my Series 3. Which leaves me needing to replace my watch. 
I’m wondering how much legit benefit there is to spending the $100 extra on the cellular model of Series 4. My cell carrier only charges $5 to tack on the watch, so it’s not that expensive - just wondering what peoples’ experiences are with the cellular watch.
Any killer features / use experience to sway my decision one way or the other?
Personally, I’d virtually always have my phone with me so the additional cellular feature would be of negligible use. (For the $120 cost of two years’ worth of cellular service I’d rather apply it to a Series 4 non-cellular watch for those years…)
To me, it’s worth the $100 plus $10/mo (for me) to be able to communicate while completely unable to goof off on a phone. I leave the phone at home about 20 hours a month and that’s enough to justify the cost for me. The battery lasts about two days if your phone is nearby, and about one day if you’re on cellular most of it, if you do about 30 minutes of recorded workouts a day. If you do really long days (18 hours) on cellular regularly you might consider the need to keep a Watch charger with you.
Overall, I recommend it to anyone who would want an Apple Watch in the first place and struggles to ignore their phone.
I love being able to leave the phone at home when I go for a walk or a run — for safety reasons, I want to be sure I can place a call if needed.
I wanted stainless steel for the more scratch resistant sapphire crystal, and the weight. That meant that I was getting cellular capability regardless, but I haven’t activated it, so I’m not paying any extra monthly fee for it. (That’s not really answering your question, but it’s part of the decision process that I went through when considering the various options)
I’ve been using cellular on my S3 for a couple months now and like knowing that I can leave my iPhone behind whenever it suits me to be distraction-free (meaning no social apps, reading, games, etc) yet still have a way for important people to get a hold of me if need be.
I’ve yet to activate it on my Series 4, but imagine I will be doing so soon.
I went with a watch without cellular features and I would do it again. Apple watch has limited capabilities for interaction, so even if I read notifications on it, I do reply on my iPhone. Calls are not that important to me, but they and streaming (if you are an Apple Music customer) are pretty much the only selling points of cellular as far as I can see. You can decide by yourself if they are worth additional battery drain and payments to your cellular provider.
I also use the cellular connection on my Watch 4 when I’m out exercising or just don’t want to carry anything in my pockets. My wife and I also use Walkie-Talkie with our watches and that app uses cellular when out of range of wi-fi.
I have the regular model and I’ve never once wished I’d upgraded to the cellular…however I’m not a runner and I do carry my phone with me at all times.
I go out every day without my phone to exercise so I get a lot of usage. Over the summer I also didn’t take my phone out most days while I went to the pool or the beach with my kids, it’s one less thing to worry about being stolen when in public, especially when you’re distracted by kids and can’t carry it on you. However, if you don’t exercise and always have your phone on you, then I can’t see the value.