This I think is relevant for all types of activities. When you create a note, or log an email, or a call or a meeting, there should be an option to “also add to associated company”.
And I absolutely agree with @Naomi: the activities should move around with the contact if it gets associated with another company. Because of the faulty automatic association, there are always hundreds of contacts in our database that are associated with the wrong company and that need to be moved around manually.
However, I think the link between the contact and its attachments should be suspended in one case: when the contact is deleted.
This is really important: When a contact leaves the company and is no longer valid for us, we want to delete it. But what about the relevant business communication? Maybe this person was involved in some milestone meetings or there is some important information in the email conversation with her. This is information we want to keep in the system - on the company card.
So in this case, there should be an option to “Keep this contact’s activities logged on the company card”.