Business owners and executives often experience bottlenecks in growth because they fail to see problems forming. Sometimes these problems develop within an organization, and sometimes they develop outside the organization because of poor customer management. Either way, it helps to have a set of 'fresh eyes' come in and identify the problem(s) hindering business growth.
Companies sometimes hire business developers as one of their services (such as banks). Often, a business hires a consultant acting as a business development expert. If you seek to work in the field of business development, you will need a certain combination of hard and soft skills. You'll also need to be familiar with specific industries and the company you are helping.