What effect does market research has on decision making?

Market research is performed in order to answer a (Yes) or (No) question in most cases. An example of the question could be: Do we launch this product or not? Should we change our prices? etc.

Those kinds of questions cannot be answered unless a proper market research is done. In this case, yes, market research is very much required because if the company were to take its chances by launching a product without doing research, the product might fail and the failure will be very costly to the company.