Jim--In long threads is that you can drop down to your last post on the list (presumably you have read up to that point) and then read from there.

It is also very helpful to see the names and dates before embarking on a list, since threads often get re-activated after long periods of time, and you can just bounce down to the recent activity--

The list is also very helpful when you want to scroll back to a re-read a post on one of those long threads--It also lets you know how long a thread is, and helps you to see whether the thread is a general discussion or is just a dialog between a couple people--

I am sure that there are a lot more uses that people make of it--