Longjohn neatly patches Node.js's asynchronous calls (like those using callbacks or Promises) to trace the full stack leading to the call, even across multiple event loop ticks. This helps immensely in debugging complex asynchronous flows by providing a complete call history. It's invaluable for pinpointing the origin of errors in codebases heavily reliant on asynchronous operations where standard stack traces fall short. Be mindful that longjohn significantly impacts performance.