Tim Hardwick, MacRumors:

Using the Segments feature in the Apple Watch Workout app is a great way to track changes in exercise intensity over the course of a workout. It can also help you find out which activities in a mixed session push your body the most.

If your regular running route includes a hilly section, for example, using segments to indicate where it begins and/or ends lets you review how much time it takes to complete compared to the rest of your workout.

Had no idea you could do this. Terrific idea. For me, this would really help with running or swimming, especially if you are doing laps. Perhaps some day we’ll see machine learning that will automatically detect the lap (when you return to the same exact location?) and break your workout into segments automatically.

UPDATE: As it turns out, AppleWatch already does stroke and lap detection (you can tell I am not a swimmer). Yet another reason to appreciate Apple Watch. Take a look at this AppleWatchTriathlete post for details.