What's the point of re-releasing an album? The original sounded good, why change something about it?

What's the point of re-releasing an album? The original sounded good, why change something about it?

重新发行一张专辑有什么意义?原版听起来不错，为什么要改呢?

-- Ritchie Blackmore 里奇·布莱克摩尔