iTunes Match is a service where music fans pay Apple $25/year to be able to upload their entire music collection to the Apple cloud and stream it from Apple's cloud to any device. Music fans can even upload & stream music they didn't buy from iTunes.

Artists like you get paid every time one of these subscribers streams one of your songs. 

There are two reasons why iTunes Match is great for artists:

1) Artists get paid every time a fan streams their song -- even if the fan already bought the song. In this case, it's like the artist is getting paid twice (once for the download, once for the stream).

2) In the event that a fan downloaded your song illegally or through some other means where they didn't pay for it -- the artist still gets paid every time that song is streamed by an iTunes Match subscriber. Which is cool.