What is Net Promoter Score?
Net Promoter Score was developed to measure customer loyalty. It indicates the likelihood that your current customers would recommend your product or service to people in their network.
Why should you measure your Net Promoter Score?
Net Promoter Scores are very effective at indicating customer loyalty (the likelihood that a customer will purchase from your company again).
It helps you identify which customers are at risk of churning. It also helps identify your promoters who are helpful for case studies and referrals.
This survey usually includes a follow up question that helps identify why customers are demoters or why they are promoters, which is equally as important.
Read everything you need to know about customer service metrics: http://blog.kayako.com/customer-support-metrics/