Well, indeed the certs issued by staging server are “real”, the same as the certs issued by production server, the difference is the CA, on staging the CA “Fake LE Intermediate X1” is not trusted by any application, Operating System, Web Browser, etc. but the certs are valid as in production it is just that no ones trust this fake CA.
Production has several rate-limits to avoid abuse. these rate-limits are higher on staging so if you want to test that your machine, your procedure, blabla works fine it is better to test it previously on staging and when you know that your procedure, etc. works fine issue it against production.
The certificates issued by production are also sent to Certificate Transparency Log which comsumes time and resources (keep in mind that we are talking about millions of certificates) so there is no need to consume these resources just because you decided to test Let’s Encrypt certs and created 14 certificates during your tests just to check if it works for you. That is the reason for staging, testting purposes. Also, the new features, bug fixes, etc. are tested also on staging server before to upload them to production.
Really, I see no concern about staging and production, staging should never issue certs using a trusted CA, that is the production’s job.