I anticipate that many Apple Watch Apps will have some sort of countdown timer. It might be to show the time until some waiting component of a game is complete, or to countdown to a special date. Either way, it sure would be nice to have something built in to do that.
That is why Apple added the WKInterfaceTimer. Before this, you would probably have to use a normal label, and then periodically update it by being triggered by an NSTimer. I haven’t done this yet, so please let me know if there is a better way for me to mention here. Nonetheless, without some fancy third-party framework, replicating the capabilities of WKInterfaceTimer was probably significantly harder.