Something magical happens when you 10x the experience, the human brain takes about 200ms to perceive anything at all — 
— Daniel Ek
Compare instant playback with the experience of manually downloading and playing music.
This 10x better UX enabled Spotify to maintain a positive feedback loop on the demand side of the network.
 possibly this is the very reason Apple UI guidelines recommend pre-loading data in making UX smooth for you, more on this here