I've had quite a few reports marked as "Good" and the post in question not deleted, even though I thought it should have been. Sometimes, as Loyce has said, the user receives a warning or temp ban instead, but we can never know that unless the user or a mod confirms it. Sometimes, if it's a whole thread, the thread is moved or locked rather than deleted. Sometimes the post has been spammy, but the follow up comments to it have been good/useful/constructive, so although the report is marked good the post isn't deleted so the remaining useful posts still make sense in context. I've also had a mod tell me that they thought it was a borderline case, so marked the report good but didn't delete the post.