Here is a description of the index-authority script.
Right now it says that "The metadata without an authority key will each be updated with an auto generated authority key. These will not be matched in any way with other existing records."
This means that if the repository has 25x "Author A.". It will be indexed as 25 different authors and it will appear this many times in the look-up UI. Therefore it would be better to give the same authority key to all metadata with the exact same value.
Of course if the metadata already has an authority key, they'll keep the same one.