There is a view of smart watches that sees them as another source of interruption, another set of notifications to deal with, another device to manage - yet more information overload. Whilst that's certainly a possibility, in my experience I've found the opposite to be true.
People have different personal requirements and usage patterns for notifications so what I'm going to outline here may not apply to you personally, in which case you personally might not find a smart watch useful. This scenario is simplified for the purposes of illustration, individuals can, and will, tune it to fit their specific preferences and needs. However, understanding the core principle here is key to understanding the value of smart watches.
Before we start I'm going to define what I mean by a notification in this scenario: it's some form of attention seeking which could be audio (e.g. a ring tone), tactile (e.g. vibration) or visual (e.g. a status bar indicator or a light). Essentially these are notifications for events that are actively pushed to you as opposed to events you pull to yourself when you chose. The choice of which category a notification falls into is highly subjective and may well change based on time (daytime, evenings, weekends, &c.), source (friends, family, colleagues, alerts &c.) or other factors (location, &c.). If you stop and think about the notifications you receive you should be able to recognise what falls into these categories for you and use this to interpret the scenario: the notifications we're concerned with here are ones you've chosen to receive, not every possible notification.
If you have multiple devices that you switch between at different times - for example a mobile, a tablet and a laptop - then the default configuration would be to have notifications enabled on all these devices so that which ever one you happen to be using will notify you.
Now you're probably not going to have all notifications on all devices all the time but the general principle is that if you want to respond, you're likely to want to use the most convenient device to do that and the most convenient device is normally the device you are using at that time.
However, as these devices won't know between themselves which you are going to chose as the most convenient one to use they all notify you just in case it happens to be them in this instance.
Lets say you're working on your laptop, you have your mobile in your pocket and your tablet in your bag. When a notification comes in it is broadcast to all three devices and they all notify you just in case they are the most convenient device. In this scenario you'd probably deal with it on your laptop. Later on you'd check your phone and clear the, now redundant, notification and later still you'd pick up your tablet and have to clear the, now doubly redundant, notification. In this scenario the addition of a fourth notification source in the form of a smart watch seems to make the situation even worse.
However, the real benefit of the smart watch in this scenario comes if we look at the problem from the other end. Rather than have the devices notify you in case they are the most convenient, you have the notifications on the watch and you then decide which is the most convenient device on which to respond.
If the response is simple - such as marking an email as read, favouriting a tweet or even just dismissing the notification - then it can be handled there and then without leaving the watch. If it is something that requires more than superficial action - such as replying to an email - and you happen to be using your laptop then you can use that but if you are walking along the street you could choose to use your mobile or if you are sat on the sofa at home with your tablet then you could choose to use that.
The key here is that you have one place for notifications that's quick and easy to check and that then puts the choice of what you use to respond to it into your control because only you know what is the most convenient device at any given time.
Now this mode of interaction may not suit you personally but, given the success of the recent Pebble Time Kickstarter, it does suit a non-trivial number of people and if you want to provide a service to those people you need to understand what it is that makes a smart watch useful and the only way to meaningfully do that is to use one yourself. If you try and provide a service to smart watch users based on how you think a smart watch is used then what you provide won't be useful.
Before I used a smart watch I couldn't see how they'd be particularly useful but now, having used one, I wouldn't choose to be without one.
Understanding smart watches isn't easy even for people who make a living out of understanding interactions with new technology.
Someone sends Skype message: 1. Mac notification pops up 2. iPhone buzzes 3. iPad in bag beeps 4. Pebble on wrist vibrates 5. repeat— Luke Wroblewski (@lukew) April 16, 2014
@lukew Consolidate your notifications. Someone sends me a message: 1. Pebble on wrist vibrates 2. I deal with it on my device of choice— Orde Saunders (@decadecity) April 16, 2014