As an owner of the Samsung Gear S3 Frontier, I feel that there are some things that the casual user should be aware of before purchasing one of their own. Now, I must say that I don't think smartwatches are bad, but there are some negative aspects that one should be aware of before purchasing one.
Price
As is the case with many new technological trends, smartwatches remain rather expensive, with the Apple Watch 3 going for almost $400! For a supplementary device that doesn't do much that your phone isn't already capable of doing, one can expect to pay anywhere from $199 to $399.
This, among other things, may persuade users with a more casual interest to wait to purchase one.
Battery
Smartwatch batteries are quite small (the one in mine is 380 mAh), though it will last through the day, but having constant Bluetooth connectivity will certainly take its toll on your phone's battery. The watch, depending on the model, may even ask to ignore battery optimizations to maintain a more consistent connection between devices than generally allowed over Bluetooth. With slightly above average usage of my phone and the watch, my phone battery won't last the day. As a result, users with shorter battery life or above average usage may want to pass on wearable technology for the time being.
Interface
Smartwatch designers must make do with remarkably little space on the devices for input and output and almost all of them do so by incorporating a dial, touchscreen, and a couple of buttons. For example, the S3 Frontier has a dial around the face and two buttons on the side, one acting as a back button and the other as a home button.
With the small screen a watch would need, the touchscreen input is generally limited to taps, offering the use of the dial as an alternative to swipes. While they are capable of more complex gestures, the watches rarely use them as a result of the screen's size limitation. Ignoring the touch functionality, the shape and size of the screen make it less than ideal for video of any kind.
With better options out there in terms of devices that offer a rich video viewing experience, the watch is certainly not ideal for such viewing.
A user with a more casual interest in smartwatches may want to buy an older model as current ones will be costly. Buying an older model will not, however, solve the issues with battery life and the interface, so one may wish to simply wait to buy future models.