Mae’r Datganiad o Ddiben yn ddogfen bwysig ar gyfer cofrestru a darparu’r gwasanaeth, o dan y Ddeddf. Mae’n disgrifio’r weledigaeth ar gyfer y gwasanaeth, anghenion y bobl a fydd yn derbyn gofal a sut bydd yr anghenion hynny’n cael eu bodloni, gan gynnwys y trefniadau staffio mewn ymateb i'r angen hwnnw. Felly, mae’n faen prawf ar gyfer arolygu’r gwasanaeth yn barhaus.
Under the Act, the Statement of Purpose is a key document for the registration and provision of the service. It describes the vision for the service, the needs of the people to be cared for and how those needs are to be met, including the staffing arrangements in response to that need. As such it forms a touchstone for the ongoing inspection of the service.