It's very important to understand the difference between deleting and unsubscribing a contact because you must ensure you do not send to contacts who may have opted out from receiving messages from you.
Deleting a contact removes them from your address book however if they are created as a contact again you may inadvertently send them another message.
Unsubscribing a contact means that as long as the recipient stays unsubscribed they will not receive a message from your account regardless of you including them in future broadcasts.