One big reason, I hate to use threading is that my reading is limited to the mails I received TODAY/RECENTLY. If a new message arrives in a old thread, it still lies way below the scrolled window and never comes to my visibility. I really like GMail at this very point and I tried to get something like this into Evolution, to improve threading usage. I got some good results.
If the message is in a collapsed state, the date of the THREAD, I compute to be the date of latest message received in that thread.
which brings the message on to the top to get the attention. If you expand, it appears like this.
If the message is in expanded state during sorting (List generation), then it takes the date of its creation, which puts it back to the original place.
Once in a day, I can use View/Collapse All and see are there any new messages to a old thread.