When buying a diamond disc, chances are, it will be dirty. This can negatively affect the sound quality of the record. However, you must keep in mind Water destroys Edison Diamond Discs! This is no joke. Don't ever clean it with water. Here is how you actually clean an Edison Diamond Disc without destroying it.
Now, your record will sound nicer and less crackly. A good cleaning makes listening to your collection much more enjoyable, and it will hopefully make you actually want more diamond discs.