When publishing a workspace from FME Desktop to FME Server, we can specify the success/failure topics to raise at the end of the execution. Unfortunately, it's not possible to do the same by using the REST API (https://knowledge.safe.com/questions/33872/define-sucessfailure-topics-when-publishing-worksp.html#answer-34135). Meaning that we have to explicitly specify the NMDirectives when running the transformation (transact or submit).
Could be useful when, for example, a team is responsible of the development of the workspace and their publication to FME Server (done inside a continuous integration/deployment environment relying on FME REST API) while a lot of different clients can consume those services and some of them will perhaps forgot to specify the NMDirectives (even if specified in the documentation). In such situation, the FME development team will not receive notification in case of failure.