So we know that the "Scan" tool is really powerful, but it is confusing to new users of Picard who think that Scan is the primary (and sometimes only) method of looking up metadata; for that reason when Scan ends up picking up files individually and breaking out from "albums" they can then say that Picard has "messed up" their files (see this recent Reddit post as an example https://www.reddit.com/r/MusicBrainz/comments/1jmexus/whats_with_music_files_or_picard/)

We already show a warning on fresh installs of Picard warning new users that the tool will make changes to their files that cannot be undone; however it might also be nice to have a "show once" dialog when you first press Scan that explains how Scan works, what it entails and maybe some guidance on trying "lookup" or using clustering instead.