If a tool helps you think, write, or build, it should leave behind artifacts you can still use when the tool is gone.
That sounds obvious, but many modern products are designed so the app is the product and the file is incidental. Your notes, links, highlights, drafts, and references live behind a login, behind a schema, behind an API you do not control.
Files reverse that relationship. The tool becomes a convenience layer over work that stays yours.
Why it matters
A file can be copied, versioned, searched, moved, archived, and opened by another tool. It can survive a redesign, a shutdown, or a business model change.
An app can still be great. But the more valuable your work becomes, the more important it is that the underlying artifact remains legible without the original software.
A useful standard
When I evaluate tools for personal knowledge or writing, I ask a simple question: if the app disappeared tomorrow, what exactly would I still have?
The better the answer, the more I trust the tool.