"Save" is cheap. "I might need this sometime later."

Delete is expensive. "Am I positive I'll never need this again?"

As a consequence, "cheap" actions (saves) accumulate, "expensive" ones (deletes) accrue until cheap becomes expensive as space becomes tight.

Ultimately, options become:

- Find criteria for rapidly assessing what data can be deleted.

- Purchase cheap archival storage and migrate old data to that.

- A media or device crash induces loss of arbitrarily-selected data.