Well, one of the things I want to do is bypass all authorisation and get the post into the database without having it trip up because a user doesn’t have permission to post into a category, or the topic is too short, or there’s not enough entropy etc. etc.
It would be nice if there was a ‘superuser’ API call which bypassed all these checks and just creates the post or topic.
For example, if you want to use the API to create a topic under a user which currently has no permission to post in a certain category, you can use the bypass_validations parameter to do this. But when you then call the API to create a reply by the same user, the validation checks are not skipped and the thread creation fails. (this is a bug which was reported 6 years ago with a pull request for a fix which never made it into the codebase).
Also, in this case, unlike with directly writing into the database, there’s no support for transactions to roll back the creation of the original thread and you have to manually find it to clean it up and fix it.