Official translations are a services only for persons who need to translate their documents to deliver them at the Spanish public service.
This may be the case of a person who want to buy a house in Spain and the lawyers ask them some official documents in order to register them to prove the information about the buyers. It could be the case, too, of a person who wants to divorce in Spain of his / her couple and then he needs to translate the official documents in order to register it at the public Spanish institutions.
Official translations can only be carried out by official translator designed by the MAEC (Foreign Affairs Ministry) who have the Official Certificate in order to translate any document requested.