This is similar to this question, but I think slightly different. When post-processing a photo, especially one taken at high ISO, how much noise reduction should be applied?
I know this question can depend some on artistic choice, and it also can depend some on the output format, so primarily I'm interested in the "technically correct" answer (so I can deviate from it deliberately instead of accidentally), as well as the most "general-purpose" answer (if I need to apply it for a specific medium, I can always go back to the original and tweak things for that format).
Edit: Based on the answers below, I guess "techinically correct" isn't the right term I'm looking for. Basically what I'm trying to get at is "How much is too much? How much is too little?" I recognize that each photo is going to be different, but right now I feel like I'm just guessing -- are there any guidelines or best practices, or default settings that people use as a starting point?