If someone replies to a message i sent to the list, and they happen to hit "reply-all" both the list and i will get a copy. Filtering on listid will send 1 to the list box i have set up and 1 copy to my inbox. First of all, i dont want 2 copies (but thats another story) and second, if it has to do with something i posted to the list, i want it in the mailbox designated for the list, not my inbox.
This is a good argument in favor of subject tagging. Or a good argument for not replying directly to posters. Or a good argument for MUA's propagating List-Id in replied-to mail that doesn't go back to the list.