Retaining a customer costs between 3 and 30 times less than acquiring a new one, depending on the industry and which studies you believe (see this great summary of studies on LinkedIn).
Regardless of the precise figure, creating customer loyalty almost always makes good business sense. Loyalty schemes encourage customers to stick with the brand and make the prospect of switching allegiances unattractive. The most effective schemes come from knowing what target customers like and expect from the brand and the kinds of practical or emotional reward they’d appreciate in return for their loyalty.
Check out 'The Smart Marketing Book' for further details.