Why to do market research for a product

There are multiple reasons why businesses do market research, and it is a wide topic to describe in one article. However, the current topic is to conduct it for a product. Why to do market research? Before getting into the topic we need to determine whether it is to understand what type of product to be developed? OR to understand the market for the product we have already decided to be developed? The clarity will drive into a right approach to do the market research.
To know market segment

Market segment is the group of people who can turn into potential customers. Understand the segment/group of customers who will buy the product, it will help us to describe what is the better fit for the identified set of customers. I would suggest getting into the shoes of a typical customer to understand the customer better. The better way of doing market research is gender based, location based, income based, age based and behavior based