We investigate the interest of migrating from a call center where all agents are pooled and customers are treated indifferently by any agent, towards a call center where customers are grouped into clusters with dedicated teams of agents. Each cluster will be called a portfolio. Customers of a same portfolio are always served by an agent of the corresponding team. There is no specialization involved in this organization in the sense that all customer portfolios as well as all agents teams have (statistically) identical behaviors. The purpose of this paper is to investigate how the benefits of moving to this new organization in terms of the management of the workforce can outweigh its drawback that comes from the increasing of variability.