Metallica has always changed up their set-list to make sure that they never play the exact same set of songs at a live performance. But now we know that they use digital music services like Spotify to fine tune their set-list for live performances by analyzing data on the most popular tracks on a city-by-city basis. Spotify CEO Daniel Ek explained how the band uses their service for song choice during an earnings call. "You have an artist like Metallica, who changes their setlist on a city-by-city basis just by looking at Spotify data to see, which the most popular songs happened to be in that city," Ek said. "We’ve never before been at a place in time where you could make as many informed decisions and understand your audience as well as we can do now as an artist."