Generally nothing, @Rob493 Air BNB has access to the payment method up to the SD limit should there be a valid claim. However, I do believe there is some beta testing that will allow the SD to be collected and refunded like most SD. At this point the former method is the primary process.
Indeed there is a change in the managing of Security Deposits. In some occasions, now, Airbnb may charge guests a security deposit regardless of the security deposit settings of the host. This will not happen to all reservations, though.