It depends on what product or service you are offering to sell or provide to your customers. It is always useful to know basic demographic information (age, gender, geographical region, marital status, etc.) of your existing and potential customers and clients. More in-depth demographic information provides details about their likes and dislikes, buying habits, etc.
Customer ideas and opinions may provide other insights into their decision-making preferences (style, color, etc.). Knowing more about your customers' buying behaviors—are they weekly shoppers, seasonal, sales only?—helps you satisfy your customers’ needs. In the end, the principle that "the customer is always right" applies here.
