Best where replacement is expensive and understanding is scarce.

Transaction engines, fee logic, customer notices, and account workflows are often too valuable and risky to rewrite blindly.

Claims pipelines, policy rules, actuarial logic, and notice systems often carry years of embedded business behavior.

Legacy workflows and operational integrations require continuity, traceability, and safer understanding before change.

Mission-critical public systems often depend on shrinking pools of experts and aging documentation.

Scheduling logic, inventory pathways, and ERP-adjacent operational systems stay deeply entangled in older stacks.

Fortran-heavy and long-lived computational systems need explainability, testability, and controlled evolution.