I don't currently have a Gear S3 but the Gear S watch. I still use and own a S7 Edge and eventually, I would like to get whatever is the latest Gear watch at the time when I do decide.
I always liked that I could leave my phone at home and still get calls/make calls from the watch from the phone and get notifications from the phone. Samsung did an amazing thing with the Gear S watches.
Yesterday while at my job, I left my iPhone in the car for half the night and the battery life on the Apple watch took a big hit because of this. Second time I noticed that the battery life suffered when not connected to the phone.
The Gear watches will do that a bit too when connected externally but that's to be expected since it is using the cell network. My watch would still easily last the full day this way. While using my Apple watch yesterday, I went back out to get my phone half way through my work shift because I was worried the watches battery wouldn't last the next four hours.