Making changes to the films outside the scope of fixing technical issues or mistakes.
Other changes - grand revisionist ‘visions’ claimed by man in charge of the studio and director of only one film… have tainted them, especially in not making availaible the unaltered theatrical originals…
(I think I may be preaching to the choir? 😃)
Or for fixing some details for consistency with other installments (e.g. like how Adywan changed the Emperor in his ESB:R to look consistent with Return of the Jedi).