[michaelt]

Some traditionalist PC users use unsaved files as sort of temporary scratch space / undo buffer.

For example, imagine you've got a template for a presentation. You open the template, you add/edit as needed, then you save it with a new filename. You don't want it to autosave over the template.

Or you need to produce a cut-down version of an internal document to send to an external stakeholder, so you load the document, cut it down, then export-as-PDF. You don't want it to auto-save the deletions atop the original.

And of course traditional PC software didn't store a rewindable document history, and exiting the software discarded the undo buffer. So if the software auto-saved a cut-down version of the document over the original, the original was gone forever.

With autosave you've got to change your way of working, making the copy before you make the changes.

[hyperknot]

Answered in detail here: https://news.ycombinator.com/item?id=42016231