The sleaziest, most dishonest, backstabbing person I ever had the misfortune of working with made frequent use of “memos to file”. Such memos can have legitimate uses, but what I’ve witnessed of them, they were most always CYA memos by someone with something to hide, and also a setup to try and blame some innocent person if higher ups ever decided to investigate questionable matters that had gone wrong.
Such docs always depend upon the integrity, or lack thereof, of the person writing.
I know someone who had had a serious enemy at work. After leaving that employ, some years later, it was learned that the enemy tried to slip something bad in the HR file. Tried but failed.
I usually prepare and email memorandum of conversation for an important talk with someone like the local tax people. And I send a cc to the person I spoke with so they can correct any misunderstandings. Good thing too. I was told last year I owed taxes from 2008 and had an email exchange from 2008 with the Asst. Deputy of Taxes to squash that like a bug.