Your customers will appreciate it. They will see that you are trying to improve your service.
You can have customers score you in different areas, then publicize your high scores in your marketing materials. It gives credibility to your statements about service quality.
It gives you an opportunity to sell something or to make an offer.
It lets you learn from your mistakes.
It helps you flag possible problem areas and clients.
It keeps you from coasting.
It keeps you form wondering what you are doing wrong.
It tells you what business you are in, and what people are buying.
Survey, Survey, Survey.