You own a big company but its core activities are not related to the tech industry (e.g. banking/ retail/ industrial, etc), and there is a business urge to develop, for example, a CRM system. Another case would be if you employ a number of HTML/CSS engineers in your tech department, however, you need to develop a mobile app which requires another set of specialists. Hiring them can be both time and money consuming, and outsourcing this task can be the best fit.