I own an Android wear watch, and I use it for three things: GPS and music while running without my phone, shopping list while buying groceries, and checking notifications when I have my phone in my pocket.
When I first got it I thought it was really cool with a small computer on my wrist and tried to think of all sorts of things to do with it, but the truth is that your phone is better at almost everything. The only reason to prefer your watch is if you leave the phone at home or if it's quicker to not take it up from the pocket. If you try do make it do too much you'll probably get tired of it, since it won't be a good choice.
Sony Smartwatch 3, and I use Google music to save a playlist offline. Subscription based streaming music is practical until it's not, and for some reason Spotify doesn't allow you to save music offline on Android wear. MP3 was so much easier when it came to portability.
I wouldn't recommend the Smartwatch 3 though. It's a pretty good watch, one of the first with GPS, WiFi and NFC (still unused), but it won't get Wear 2.0 and the GPS ranges from pretty bad to unusable. The GPS antenna can't handle when your arm gets wet, like when you sweat, so after about 20 minutes of running the GPS connection deteriorates significantly unless you have a sweatband under it.
Hopefully Garmin will launch a watch with Spotify support in the future.
When I first got it I thought it was really cool with a small computer on my wrist and tried to think of all sorts of things to do with it, but the truth is that your phone is better at almost everything. The only reason to prefer your watch is if you leave the phone at home or if it's quicker to not take it up from the pocket. If you try do make it do too much you'll probably get tired of it, since it won't be a good choice.