Copying in a comment from another thread with @nwolfe on the same topic...

Some of the shutdown tests make use of the "true" flag for `return-app-on-service-error?` for forcing the Trapperkeeper app to be returned to the caller. See the bootstrap-and-validate-shutdown function in "shutdown_test.clj". This is done so that the function has a handle to the app that it can use to call `run-app`, testing that `run-app` has detected a shutdown error and translated it into an exception thrown back up to the caller.

For the most part, I think tests would use the "false" flag but broader component tests like the ones in "shutdown_test.clj" needed this.