It is standard practice within all federal departments. It’s a law.
I was once involved in the management of a relatively small internal program at an agency that the IG decided to audit. The resulting report showed an amazing lack of knowledge of the complexity of the program and its purpose. We met with the authors of the report and had to school them on numerous aspects of the program. I almost felt sorry for them because of their general lack of knowledge and technical competence. The IG subsequently made significant revisions to its report and, in the end, it was all a big nothing burger.
Given the small size of the program, which was of a temporary nature, I always suspected that a resentful “tipster” had it in for a person higher up in my chain of command and called the IG. Either that or the IG was looking for something to justify its existence.
Despite that unfortunate experience, IG’s often do produce useful and constructive reports.
I was the subject of an IG investigation by the 49th Armor Division IG while deployed to Bosnia in 2000. He interviewed me, and I never heard another word about the investigation. Several years later, I received a letter from the Army IG, stating that the 49th AD IG had found me to be negligent, and filed their findings against me, but after a review, the Army IG found no wrongdoing on my part and were deleting the 49th AD IG report from the public record. So much for providing findings with the one being investigated. Fortunately, Big Army IG was more competent than the 49th IG.