In a shared services model, work that was previously duplicated inside each business unit is pulled together into one center that provides it as a service. The business units become internal customers, and the shared unit is accountable for defined service levels.
The gain is twofold. Consolidation removes duplicated effort and standardizes how routine work is done, while a service orientation makes cost and quality visible in a way scattered support functions rarely are.
The model is a structural choice within the wider operating model. It works best for activities that are common, high-volume, and rule-based, and less well for work that needs deep local context.