The big consulting firm runs a program/project to deliver a result. Perhaps implement a new business system or technology or integration, optimize or implement a new process, perform some organizational change in the way things are done, etc.

Companies don’t have the skills or experience or expertise or resources or time in-house to do it themselves, so they essentially outsource the initiative or objective to a consulting firm.

It’s seen as less risky to go with name brand big consulting firm. But companies think they can pay little and get a quality delivery team, and the big consulting firms usually find a way to make a profit at the expense of quality by leveraging inexperienced consultants or consultants overseas with no real world experience.