I think there is a difference between using it to support debugging SNAPSHOT builds (which I do not care for) and providing additional information for QA builds (which I am a huge fan of). Consider the case where you fire up a 24-hour ingest test, and it errors at the end with something arcane. Meanwhile, other people have been adding code and your workspace copy no longer matches what you deployed. Having the git commit may be helpful to track down a revision from that point.
I'm not sure I understand your concern about not being able to reproduce source releases. If the code is tagged, then it will always have the same commit id, which will always be the same, every time you check it out. If anything, I believe it adds to the release process, as an extra verification in the artifact that shows "yes, this came from the source I claim."