On the Campaigns -> Import/{Integration} -> Requests page there are two options under the Unsubscribed column. They are Unsubscribe and Block. 

Unsubscribe will prevent the patient from getting any further requests as part of a campaign.

Consider a visit type called Spam that is set to receive a request on the same day as the appointment (Delay 0), receive a follow up everyday for two weeks (Frequency 1 and Length 2 Weeks).  The practice hears from Patient Bob that he is going to be away for the next two weeks.  The practice doesn't want to fill Bob's inbox with 14 requests.  They would use the Unsubscribe option.  That stops the sending of any further requests as part of the Spam campaign. The next time Bob visits the practice for a visit that is set to receive a review request he will receive one (assuming Duplicate filter is off or the six months have passed)

Consider that same Spam visit type. This time the patient, Dorothy, has already received several requests and asks the practice to never send them another review request, ever again.  The practice would use the Block option.  Dorothy would never receive another review request at that email address.  Another reason a practice may want to use the Block feature is with a patient who is difficult.

For SMS, Unsubscribe and Block work the same way, preventing a patient from receiving any future requests.