Why Exactly Is Spotify Being Sued and What Does This Mean?

On December 28th, 2015 long-time streaming foe, David Lowery, who runs the Trichordist blog and fronts the bands Camper Van Beethoven and Cracker, filed a class-action lawsuit seeking at least $150 million in damages against Spotify. The lawsuit alleges that Spotify knowingly, willingly and unlawfully reproduces and distributes compositions without obtaining mechanical licenses.
Ok, so those are the facts, but what does this mean?
Just for some basic background which will come in handy in a bit