Delphi XE with Firebird Database, Datasnap Driver, DataSnap Service vs other schemas when working for mobile apps

I`ve found out that most of the time it is recommended to use this schema when connecting to a localhost server.

Not necessarily Firebird as Database, but the Driver and the Service are always recommended to be Datasnap.

Why to use a Datasnap service instead of, E.G., the Firebird service that runs by default in the database host server? Is creating the Datasnap server a really required extra feature?