With a large number of local folders, going through the entire classification tree for every single email which should end up in the same local folder is boring... (for example one original email and its answer are in two separate Imap folders : Incoming mail and Sent. I cannot select them at the same time and direct them to the same local folder once treated...
Mail.app has this function : "move to the last folder used", and once a series of email is treated, sending all the series of emails to the "last folder used : XXX" would save time.