Concept of IAM Architectural patterns took years to reach maturity sufficient to be published as a form of best practices for corporate Identity and Access Management. Architectures described here apply to small and large enterprises, however smaller companies may not directly see the consequences of bad implementations and may not consider IAM Architectural patterns implementation leading directly to reasonable ROI.
Historically IAM evaluated from meta-directory solutions, automation and certification components. They aimed to enforce responsibility for IAM managed entities therefore improve security and operational efficiency within organizations.
Historical background that includes various paradigms such as RBAC / ABAC or discretionally access controls left IAM hanging in No Man's Land between business and technical end-points. This is one of the major drivers that let companies see IAM to be crucial but hardly achievable via IAM systems.