Blacklists are an extremely important feature that avoids interacting with the same users. Users that are added to the blacklist won't be followed and their posts won't be liked or commented on. Basically, they won't be interacted with anymore. The blacklist feature can found in almost every single module and works as expected except for in the unfollow module. The unfollow module ignores the blacklist completely except the Add interacted users to blacklist option which causes users that are unfollowed to be added to the blacklist.
The whitelist can only be found in the unfollow module and its only purpose is to let the unfollow module know which users should NOT be unfollowed.
So to recap: Blacklisted users will be ignored by every module except for the unfollow module which will only look at the unfollow module to know which users to ignore.