A few days ago, a user came to the helpdesk with the issue that their most recent changes to some Word documents had been lost after they rebooted their mac.
I started digging, and found that there was no version history - which is unusual. My org is mostly a Microsoft shop, and by default their org-licensed copy of office should create new files in OneDrive. I took a look at the Save settings in Word and found everything unchecked. It looked something like this, to give you an idea of what I mean.
I hoped maybe they'd managed to save their files to their personal iCloud account^1 since they were using a mac - no dice, they had an iCloud subscription, but they'd disabled syncing to iCloud.
And as I was expecting by this point, they did not have the OneDrive desktop client installed. It wasn't just that they had never signed in - it wasn't installed. Which means it must have been manually be uninstalled, since it's part of the Office suite.
So it seemed like a reasonable case of them following the bad practice of only saving work locally on their machine. That stymied any recovery efforts, but why had the work been lost in the first place?
I asked the user to show me how they normally go about saving documents. They brought up a Word document that they were currently editing.
It was a new file, and had never been saved. They had written about 12 pages of text, and it basically only existed in RAM^2. Apparently they'd had this document open since the aforementioned reboot, which was several days prior.
I thought I was used to this sort of thing by now, but I found myself needing a few seconds to process and mentally press ctrl-s/cmd-s a few times in prayer.
I explained as diplomatically as I could, that because they weren't using any of the auto-save or cloud options, they needed to manually save their work.
Thankfully they were amenable to using OneDrive and I got it set up for them, so even if they learned nothing they might be OK for a while.

EDIT: I almost forgot the weirdest detail - it turned out their actual 'saving' process was to copy-paste the entire document and airdrop from their mac to their phone, to send in an email. I'm still not sure how anything was saved on their laptop to begin with.

^1 During the course of troubleshooting I learned that iCloud's auto-saving features only apply to Pages, not Word - but moot point since they'd turned it off in Settings anyway.
^2 I know that's not quite how it works due to the local autosave and filelocks and whatnot, but for practical intents and purposes... no doubt they would ignore an 'unsaved work' prompt when closing Word too.