Best-of/compilation/greatest hit collections are someone besides the listener (or the band, usually) deciding which songs are the best that a band has done, isolating them, and expecting people to pay for them. If they really have a lot of balls and too little respect for fans, they'll put brand new songs on the collection so people who already have all of the material and their own opinions of what should be on a best-of are pressured into buying a lot of shit they already have to hear a little bit they don't.
It is all a marketing scam.
It is all a marketing scam.
