Service staff are trained to deliver excellent customer service. What is the purpose of this?

To achieve or arrive at customer retension and customer loyalty. Once service staff are trained to deliver excellent customer service & they actually provide it, customers are satisfied & delighted. When customers are satisfied & delighted, they will be loyal or repeat customers thus the customer base will be maintained & further expanded as the current customers will provide a testimony to the public of which more prospectice customers will be lured & enticed to join the customer base.