The problem is that to monitor your sleeping patterns, a valuable feature most of these new smartwatches support, the watch needs to be on your wrist. So leaving your watch charging overnight while you slumber isn’t going to work. But smartwatches have small batteries compared to smartphones, so should only take 2 - 4 hours to fully charge, depending on the model.
Finally, Wear OS has a problem that’s seemingly random and hard to understand: “Can’t reach Google at the moment.” Having tested at least a dozen Wear OS watches, we can say that an unexplained failure when using voice commands is the most common negative trait for all of them. It’s impossible for the layperson to understand which part of the watch-to-phone-to-Internet relay is falling down, but it can happen at any time, even right after you’ve used the watch to do something else successfully. When Google Assistant is made the center of Android watches, not being able to reach Google Assistant lowers the value of that watch considerably.