To be able to unmerge contacts.
It is often an issue if two different contacts use the same browser, where their activity feed would be combined. To be able to check off which entries you are moving to a new contact, then create that new contact and have those chosen activity fields populate the contact properties would be AMAZING.
Right now this is a huge inconvenience and manual process to create the new contact, and their activity still shows up on the original contact's page. This messes up analytics.