If you are _already_ administering an existing setup, or have a custom automated deployment of a service, probably not much.  When you need to deploy a new service, the roles should save you work because a lot of the "custom" work is really common to most deployments and shouldn't need to be custom; or if you were new to Linux system administration, the roles should simplify everything (but not make it impossible to deal with the details).

    Mirek