Okay, so that camera voice command Google pointed out the other day wasn't terribly useful, but the new music command is pretty cool. Just pull up voice search in whatever way you prefer, and tell your device to "play some music." That's it – the tunes will flow.
— A Googler (@google) March 21, 2014
This action immediately boots you into Google Play Music and starts I'm Feeling Lucky Radio. If you have All Access, that playlist will include a wide selection of content based on your listening habits. If not, it's just the music you've uploaded to Google Play Music.
It saves you a few taps and it's a neat trick for parties. This and the camera thing seem geared toward Android Wear, but it's still cool on a phone. Enjoy.