It is very important to edit permisions not only to the whole contact but only to the specific activities.
In our situation we have several sales reps. They have to see all the contacts to know what was the comunication and who is the owner of the specific contact. But we don't want to give junior sales reps access to the emails body.
We regularly have inquiries by law enforcement agencies on specific customers. These inquiries are confidential must therefore be kept from most sales and service agents.