Always. If someone has an opinion on a subject I am interested in, I want to hear it.
Most of the time it is mindless conjecture, "You're an idiot that don't understand nuffink" type thing, but sometimes it is valid discussion with, arguably, poor word choice that is being punished with no sense of context. An example:
"You're a moron." A comment casting character aspersions on another; in my opinion an instant suspension for showing no respect or tolerance.
"Don't be a moron." A comment that implies that you feel someone is selling themselves short by not articulating their point properly and therefore should only be moderated if it is not backed up with considered opinion.
Also, take the tone of the thread into account. If the original post is "What is your favourite cheese?" then don't moderate someone for low content posts, but do moderate someone who has nothing to say other than the discussion is pointless/illogical/trivial. IF YOU FIND THE DISCUSSION POINTLESS THEN DON'T FUCKING JOIN IN!
Also, also, why is saying "that made me laugh", "I agree" and so forth, given low content warnings, but 'Grammar Nazis' get away with adding absolutely nothing to the debate?