Bots are a good thing because they can do boring (easily automatable) stuff much more efficiently than humans, so that they can concentrate on more interesting/complicated edits. However, they make mistakes, and some mistakes are very hard (if not impossible) to fix. Reasons include:
- Errors in other databases: A bot trying to link to Discogs can't know if the Discogs release is faulty. And it is not always possible to fix the other database.
- Matching thresholds: When matching by similarity, usually bots have some thresholds. They often have to be lower than 100% so that they doesn't exclude too many positives, but it can't be guaranteed that they won't have a (very) small percentage of false positives then.
Edits like this are usually entered by bots as normal edits, so editors can (and should) vote them down. Clever bots have a persistent memory of the edits they made, and won't do them again. And here is the problem: If some other bot author at a later point of time runs the same (or a similar) bot, it will probably make the same error again (and again and again).
To give humans a chance to defend themselves against this problem, there are blacklists for certain kinds of bot edits. If you want to protect a MusicBrainz entity against future faulty bot edits, enter them in the corresponding list. Bot authors should download the appropriate blacklist before every run, and omit edits that are listed.