For a new project on BAW v21 the honest answer is almost never - client-side human services (CSHS) plus service flows cover everything heritage human services (HHS) did, and IBM has deprecated HHS. The few cases where an HHS still comes up:
- Heritage coaches you must keep - an HHS is the only container that can run a heritage coach (Coach Designer 7.5-style); CSHS cannot host them.
- Server-side script between coaches with full JS API access - in an HHS every script runs on the server with tw.system, Java integration and SQL in the same flow. In a CSHS the scripts run in the browser; server logic goes into a service flow called from the CSHS (one extra artifact, but the right split).
- Old toolkits that expose only HHS for reuse (some vendor toolkits, older Salient or IBM samples).
- Exposed as URL with server-side pre-processing - HHS "Startable" services used to be a quick way to run server code from a link; today use a startable CSHS with an initial service flow, or a REST-exposed service flow.
What people wrongly believe requires an HHS: exposing a service as a dashboard (CSHS can), calling a Java integration (service flow can), document handling (service flow + UI Toolkit document controls), timers inside a UI (client-side timer control), custom HTML (custom coach views).
Migration note: BAW converts most HHS automatically (Convert to client-side human service in the designer); heritage coaches must be rebuilt as coaches with coach views. On CP4BA / Workflow Process Service, heritage human services and heritage coaches are not supported at all - a reason to avoid new ones.
References