DocumentMode - written in the third person and left unsigned. ...it may have multiple and changing authors as it is updated to reflect the community consensus. This is in contrast to ThreadMode, comments which are usually signed and in the first person, and rarely edited by people other than the one who signed them.
Wiki excels at DocumentMode. Many pages start off with an Opening Statement which declares a piece of wisdom. It might be a pattern,... a question instead of a statement, ...an opinion, phrased strongly to invite feedback. The rest of the page may then be the feedback: clarification, comments of agreement or disagreement, supporting evidence...
Often the feedback is in ThreadMode. Sometimes, after a discussion has reached a consensus, someone (could be anyone), will delete it and post a new Document Mode contribution which incorporates what has been learned.
A good DocumentMode comment is easier for newcomers to understand than a ThreadMode one. Threads are full of transient misunderstandings and special cases. The important points don't stand out well. And they are full of egos. The valuable content of Wiki ought to find its way into DocumentMode comments. It doesn't, always. We need more Wiki:WikiMasters.
ThreadMode comments are usually shorter than DocumentMode ones. If you find yourself writing a long reply, consider writing it in document mode, or even making it the OpeningStatement of a brand new page (with back and forth links to the original page, of course).