The most successful business projects are always those that are driven by an employee who has the authority, vision and influence to drive the required changes in a business.
It is highly unlikely that a business owner (decision maker or similar) will realize the changes unless one has one of these people in the employment. We therefore like to engage our consultants in house so that they can operate as a person on your companies payroll.
However, the project leadership role typically requires significant experience and skills which are not usually found within a company focused on day-to-day operations. Due to this requirement within more significant business change projects/programs, outside expertise is often sought from firms which can bring this specific skill set to the company.