At the base level, smartwatches are designed to provide information to the owner with just a quick look at the watch face. On the Apple Watch this is augmented through two different features -- Glances and Complications.
Glances are aptly named as they give a screen of basic information from apps with just a swipe up on the watch face. Any app can have a glance mode if the developer builds it into the app. Many apps are already getting Glances incorporated and they are handy features for all types of apps.
Complications are a different beast, starting with the strange name that Apple has chosen. Many Apple Watch faces have tiny areas on the display that can show information at a glance. These info gizmos currently consist of calendar events, local temperature, and watch battery level but can be anything the developer wants to present.
These can be selected by the user on the watch face selection screen by tapping on a Complications area and then spinning through the available information options with the Digital Crown. This allows having just the information that is important to the watch owner, and it's a useful feature as Complications are just a quick look at the watch away at all times.
Sadly there aren't yet a lot of apps that have Complications available. This is unfortunate as Complications put apps front and center in the face of the user which should be what developers want. They could be especially useful for business apps.
See related: Tips for using the Apple Watch for work
I see a big benefit for apps such as those used for team collaboration to have Complications that can be put on the watch face. Imagine glancing at the Apple Watch and seeing the next task for the team that needs to get done. Or a reminder to call a workmate for information.
The uses for Complications are only limited by the imagination of the app developer. Properly conceived and executed they can be as useful as the Apple Watch Glances, perhaps more so given the in-your-face nature of Complications.
Because Complications sit on the watch face they are particularly useful when used with the watchOS 2 Time Travel feature. This is the function that lets the user rapidly move time forward and information displayed in Complications moves along with it. This permits seeing future calendar events, for example, when normally only the next event is shown. This would be very useful for CRM apps, letting the sales rep spin forward in time to see upcoming sales calls.
To provide maximum usefulness for an app, developers should be producing all three tiers of benefits for users. Those are to first support the Apple Watch with the iPhone app, next to add a good glance option to the app, and finally to build a complication that makes sense given the purpose of the general app.
Adding support for Complications makes good sense for developers as it puts their app on the watch face, and Apple Watch owners look at this dozens of times each day.
Developers who fully support the Apple Watch will find that watch owners are going to gravitate to them over apps that don't. These watches are not toys when properly leveraged, and good apps will let owners do that.