For class discussions I use the nested view. But when messages start to pile up it becomes harder and harder to get a sense of the discussion, for two main reasons: 1) since the view is exploded one has to do a lot of scrolling back and forth when exploring the discussion; 2) most people don't bother to put meaningful subjects and thus one frequently has to re-view more than a message's subject to recall what is it about.
2) Remove the default 'Re: xxxxxx' subject and use instead the opening of the message body. The subject text field in the message edit window should be empty by default and not forced. If the message is posted with no subject, use the first, say, 60 characters and add '...' to indicate that there is more.
What do we get?
When I open the forum I can refresh my memory of previous discussion by reviewing the messages' titles. Note that now the titles view gives a better sense of the ongoing dialog since the titles are the openings of the messages rather than a repetitive 'Re: xxxxxx'. Since the forum is collapsed (or at least can be collapsed) many message titles fit into the window frame so I need to do less scrolling. If I want to read a certain message I simply open its body so I can see the message but also the other messages' titles. Since I'm in the same view I can scroll to nearby messages and open them too if I want to compare their content.
The above approach is perhaps not so important in professional 'I have a problem' kind of forums but is crucial for online discussions in Arts faculty courses.
A comment about the 'Re: xxxxxxx' feature.
This is probably a remnant of email based discussion groups. But it should be obsolete by now in LMS environment. If I use the nested view, I can see for each message to which message it is a reply. If I use the flat view then all messages are replies to the topic. So I don't need the subject to repeat that.