logging statuses that were typed out, but ultimately not posted.

That’s common practice across the web. For example in a lot of social networks (not Lemmy) if I were to close this reply box without clicking the “Reply” button, I’d simply be able to open it and my half written reply would be restored.

It’s not about gathering data on users, it’s about saving users from accidental deletion particularly on touch screens where it’s so easy to accidentally brush the wrong button.

Logging key strokes is different, there’s no reason to record that anything you record (other than actually typing messages) is likely to be something the user intended to type somewhere else but didn’t realise which browser window had keyboard focus.