Chat is completely Ask Ubuntu RealTime Edition™ - that's what chat's for. Chat should ultimately facilitate everything Ask Ubuntu is and does. This should include meta discussion, community building, and support. Comments, the second class citizens they are, sometimes don't cover the bridge that's needed to really troubleshoot an issue. That's where chat can play a vital role in getting an exchange of comments done in realtime.
Often users stumble in and ask for support directly. If it's an easy one-off question there's no harm in just saying "oh, do this". However, I've made it a practice that if a user comes in with either a question that is complex, or one that can benefit multiple people, that they first ask it on the site, and come back to chat with a link. That way a discussion can occur, when new details are found out the original author is request to place it in his question, when an answer is discovered whomever found it is encouraged to answer it on the site.