not just money. How are you going to support this client’s support ticket if there is no log at all?
Sure it is a possibility that the ticket will end up closed as “unable to reproduce”, but that is always a possibility. It is not like you have to shut off all support because that might happen.
Plus many support requests are not about the content of the api responses but meta info surrounding them. Support can tell you that you are over the api quota limit even if the content of your prompt was not logged. They can also tell you if your request is missing a required parameter or if they have had 500 errors because of a bad update on their part.