Data mining is the practice of examining large pre-existing databases in order to generate new information or to predict future trends. It is useful because: 1) it helps in identifying the multi-dimensional patterns of large data, 2) establishing relationships, 3) putting together predictive models, 4) customer data can be mined to acquire new customers, retain customers, cross-sell to existing customers, 5) helps financial sector companies build fraud detection models and risk mitigation models, etc. Skills required for data mining are statistical knowledge, artificial intelligence/machine learning, and competency in Python, R, and SQL; also along with these technical skills a data miner should have business knowledge and other soft skills. Read more at: http://www.datasciencecentral.com/profiles/blogs/data-mining-what-why-when