Implementing a shared service model is a difficult process and consists of many different components. Being a shared service provider is comparable to becoming a supplier, and most IT teams cannot easily convert.
Most companies want to reduce costs by providing a shared service model. Adopting a shared service model does not always result in these expected cost reductions. Simply combining the operations of two IT organizations does not necessarily lead to economies of scale and cost efficiency. Before implementing a shared service implementation, determine if the project will bring value to your organization.

Source: www.infotech.com