Smart watches like the pebble can be amazingly useful in certain circumstances. For example, if you're very busy and using some sort of messaging system to stay in touch with a team then a smart watch is indespensible. You can keep up with the message flow without digging out and unlocking a phone. It easily replaces radios without many of radio's downsides and with many unique advantages (archived messages that can serve as a reference later).

I don't know how useful they are in the general case though. But they do lower the friction of keeping up with a textual conversation without being in front of a computer.