Most often for obvious bad-faith arguments, such as clinging to misinformation or logical fallacies despite having them pointed out as such. Sometimes for extreme rudeness toward another commenter (not a public figure). Never for mere disagreement. Also never for "not adding enough to the conversation" because I think the hostility toward short comments and "small talk" here drives every conversation toward pompous verbosity. There's nothing wrong with a "lighter" conversational style.