I'm not sure if my input is of value, but I'll press ahead.
Obviously it is useful for admins, we can quickly take a look at the tone of participation throughout a thread for an individual member.
For long discussions, I find it is useful to read all the posts of my principal opponent as a means to understanding their position as a whole which helps me understand an individual comment made in their most recent reply. If someone is making lots of posts, and is getting dog-piled, it helps me not to ask questions that person has already answered and to cut straight to addressing their answer to that question.