Some wikis use a mechanism where FlaggedRevs can be configured individually for each page. On the English Wikipedia, this is called Pending Changes. Pending Changes level 1 (PC1) is currently in use.
When PC1 is enabled on a page, accepted changes are highlighted in light blue (tested: MonoBook, Modern and Vector skins). The presence of white lines (usually reverted changes) is a helpful visual hint that PC1 is indeed needed and should continue to be used.
When PC1 is then disabled, the highlighting of past edits is removed. However, continuing to display that information for those edits to whom it applied when PC1 was active should be the default. Removing the information conveys no discernible benefits, while retaining it more easily shows the extent to which protection measures may be warranted. I suspect but have not tested (for obvious reasons) that if an admin were to misclick and disable PC1 by mistake, the historic record would at once become unrecoverable through the UI accessible to admins, even if PC1 were re-enabled. Only new changes would then be highlighted again.
(Additionally, but not quite so importantly, when PC1 is active, the usernames of who accepted certain changes is also displayed, or a note that a change was automatically accepted, for those with sufficient privilege. This display is also lost when disabling PC1.)