The current crop of standalone smartwatches (Urbane 2, Sport, Gear S2 and S3) have a functionality equivalent to a flip phone. In a form factor that's smaller and more convenient. They can handle calls and texts, provide time, date, weather, and run simple apps like calendar, reminder, stopwatch, etc. For those whose needs are basic, these watches can be an only phone.
If more advanced functionality is needed, they can be remotely connected to a smartphone (that doesn't need a SIM, just access to WiFi) and never leaves the house. As more standalone apps are created, the watches will become increasingly more capable.
I've found that wearing a phone is much more convenient than carrying one. There were many instances when I didn't have my phone on me. Lounging around the house or yard, my phone was frequently in a different room. Once or twice a month I'd leave the house only to realize later that I'd forgotten my phone. Then there were occasions when the phone was a hassle: at the gym, wearing skinny jeans, or being out on the water.
I no longer use a smartphone. I strap on my watch in the morning and never need to think about where's my phone. Of course there are tasks that can't be done on a watch. I keep an LTE tablet close at hand for composing emails, watching videos, reading eBooks, surfing the web, running apps, etc. What I used to do on my smartphone is now split between my watch and my tablet. Less compromise, more freedom, and greater efficiency.