1. Fitness tracking
Current smartwatches are a bit behind dedicated fitness wearable in this department, but you can still do a surprising amount. Most Android wear watches and the Apple watch come with an okay heart rate monitor and the ability to track steps more accurately than you might think. From smartwatch, you can get metrics on how many calories you've burned, how far you've run and much more.
2. Media controls
Yes, this is not the world's most amazing feature - heck, it's built into quite a lot of headphones already, but it sure can be useful. Rather than having to pull out your phone every minutes to adjust the volume or skip a track, you can simply lift up your watch and adjust it all from there. This probably is not a huge deal if you've got your phone out and on a desk, but if you are on public transport or, really any other situation where getting your phone out might be somewhat inconvenient, it can be a lifesaver.
