When Not To Use This

Do not use a custom outcome type when Result would do. ? already works on Result, and most public Rust APIs should expose ordinary error types.

Do not use outcome types whose short-circuit case is common. ? hides the branch, so frequent control flow deserves an explicit match.

Do not put these types in public APIs of widely used crates unless the semantics are central to the crate. Callers should not have to learn a new meaning for ? just to use a basic function.

Do not compose outcome types when residual semantics conflict. If a function wants to return both parsing failure and cancellation, pick one outcome for the function body and convert at the boundary.

Do not use Stage when a plain state machine is clearer. Stage is useful when partial state and resumption are part of the contract, not when the code only has several helper functions.

Do not use Checked<Finite> as a general numeric tower. It is a narrow tool for making invalid floating-point results visible in ?-driven code.