You obviously have to decide it on a case-by-case basis. But anything that is only used in a comparison is usually fine with saturating. And many things that measures values or work with measurements are fine with saturating if it's documented. Saturating is how most analog equipment works too, and in non-interactive use cases "just pick the closest value we can represent" is often better than erroring out or recording nothing at all.
Of course don't use saturating_add to calculate account balance, there you should use checked_add.
