What you you mentioned is not true. You could have only three cancellations in one year if you have instant booking turned on. However, you better to call Airbnb to cancel a confirmed booking because many hosts had posted here about their mistreatment by Airbnb after they canceled a reservation even though they had instant booking on.
I did InstantBook for about 1 day, then gave up when the first person who booked used someone else's account to book. That was a whole charade trying to get that straightened out. Occasionally I have someone wanting to bring pets to my no-pets stay, or 4 people to my max 2 people stay, etc.
InstantBook is puffed up by Airbnb as a way to increase your bookings. Well I do just fine without InstantBook.