Once the songs are downloaded, they may be played at any time. The technology of MP3s is being used to download songs for the user's listening pleasure. The MP3 downloads are free access to the songs, meaning that the CDs from the artist do not have to be purchased. The copied copyrighted songs are free and the music industry and artists receive no money from the use of the song. According to the RIAA, Napster is a big automated way to illegally copy copyrighted materials.
Users love it because it's free, the music industry hates it for that same reason.
Napster's defense is that the files are personal and on the users own machines and they aren't responsible. The copies of copyrighted songs is copyright infringement. Napster operates in a gray legal area, as no copyrighted music actually resides on its servers. It keeps track of all the online users, no MP3 files are on the servers. Napster is not the distributor of the songs, it's users are.