This is one of the guidelines in wikinomics.

In a wiki, comments should be used to compliment collaborative editing not as an alternative to it.

Use comments to:
*describe changes in your previous edit, an edit comment.
*have a meta discussion about the page itself (or create a talk page).
*ask a question.

Avoid using comments to:

*give your opinion or make remarks on the topic. Ideally you should be bold and edit / append your ideas into what others have written already. If not someone will do it for you.

Comments are editable too!

A great feature of socialtext is that comments are not locked away in some external box on the page you can't edit. They can (and should) be refactored, absorbed or digested. If they don't apply to the current version of the page they can be removed.Removing a comment once you have responded to it is probably a best practice.