Apples smart watch will be absolutely amazing because they actually know what would make a device like this incredibly useful, and almost vital to have (unlike the galaxy gear which is honestly an embarrassment). That of course is biometrics, health sensors galore, I can't possibly explain how overwhelmingly amazing and important technology like this would be if it is highly accurate and widely purchased.
Most people don't understand or can't grasp the usefulness of this, or all of the possible uses for it. If they can put highly accurate health sensors in this product that one will wear almost 24/7, which can graph and analyze health data attained by it, it will not only make life much better for millions of people, but it could save lives. Just as a random off the top of my head example, an elderly person could be wearing it and if they went into cardiac arrest it could instantly send an alert to family members devices so they can call 911, or contact health services itself if possible.
If they were to have highly accurate non-invasive glucose monitoring, it could augment or possibly even take the place of invasive glucose monitors for the millions of type 2 diabetics (which is growing all the time). Glucose monitoring wouldn't just be useful for diabetics, it would be useful for any smart human to test their blood glucose and get an understanding of what their bodies can and cannot handle, carbohydrate wise. Beyond that there are so many possible applications I can't go into them all in one post.