Dear Yugank
the "classical" application for sentiment analysis is social media monitoring, where companies track how their brand or products are discussed in Twitter, Facebook etc. This helps for instance to assess the value/effects of marketing campaigns.
But there are also other applications: It is also used in customer support to find ot "how upset" a certain customer is, and the offering these customers a certain discount. And one of our partners used sentiment analysis in a bank, where he analysed the sentiment of messages from private banking customers to predict the revenue with each customer.
Best wishes
Mark