The Service Specific Access control is mainly for the disasters conditions. For instance Tsunami or Earthquake or any terrorist attack. In these conditions the Operators can restrict some services of the users. It can stop the non voice calls and only allow Voice because that would be demand of situation. Uninterrupted communication is main concern in these circumstances. Similarly for the users who don't have sufficient money in their account they can give some relaxation in those cases.
The provider can choose to shut down the service if the requirements is not meeting up the situation. It is up to National Authorities to define and implement in such cases.
For reference: Study on Service Specific Access Control
