@Edent I think @ostephens means that because you use the CW effectively as a subject line, some clients when they expand the CW-ed post will hide the CW itself and therefore the subject of your post.
(Whereas some will expand the post but leave the warning in place, still readable. I've tried a few clients so far and seen both behaviours.)
@benjamineskola @ostephens Oh, that's interesting.
I mostly use the web interface. I don't think there's a right or wrong answer.