I've just moved over from Forte Agent. Thunderbird doesn't do everything I'd like it to but there's one specific action that seems to me like a timesaver.
Forte Agent allowed incoming email to be assigned a specific folder so that all emails from and to a person could be collected together.
There was a setting in the Address Book where it could be manually assigned or the program could be 'trained' by dragging an email into an active folder and the recipient (email address) would be remembered.
So, all my emails from and to 'John Smith' went into the folder that I'd created called 'John Smith'. It saved having to drag them there and to have to retrieve them from 'Sent' if I initiated one.