This information I came across at Wikipedia this week:

There are several factors that make the interim management offering increasingly popular and cost-effective to client organisations. These factors are characterized as a ‘value proposition’ that interim managers offer to their clients.

Although there is some variation at the margins of interim management (with temporary workers, freelancers, contractors and consultants) the following factors are typical of the interim management value proposition:.[7]

1. Interim managers can be in place within days as opposed to weeks or months, which is essential when time constraints are paramount. Being practiced in engaging promptly with the situation, they become effective quickly upon joining a client organisation. Because of their experience and expertise, interim managers also conduct and complete assignments effectively and with due speed.
2. Interim managers typically operate at a senior level in the client organisation, often being sensibly over-qualified for the roles they take on. They often bring skills and knowledge not otherwise in place, to address a specific skills gap or problem. Their experience and expertise enables them to be productive and make a noticeable impact from the outset, maximizing the likelihood of success.
3. Unencumbered by company politics or culture, interim managers provide a fresh perspective and are able to concentrate on what’s best for the business. Being independent operators, they are able to contribute honestly without constituting a threat to the incumbent management team. Not being part of a larger business they are not pressured to unnecessarily extend their assignment.
4. Rather than taking on a purely advisory role, interim managers are managers responsible managing a particular business or project. They are accountable for results.
5. Operating at or near board-level gives interim managers the authority and credibility to effect significant change or transition within a company. Unlike a ‘temp’, they’re not just there to ‘hold the fort’. They actively add value to the client organisation as a result of their expertise and approach, even when the work and the decisions to be made are difficult.
6. Interim managers add value by using their skills and expertise to help deliver an outcome, solution, service or mitigate risk that provides a meaningful ‘return on investment’ to a client. Interim managers are paid on the understanding of goals and objectives being performed and delivered, and not simply on the basis of attendance.
7. Interim managers maintain high professional standards because their future work relies upon referrals and a successful track record. They therefore have a stake in the success of the assignments that they undertake. This contrasts favorably with other ‘temporary workers’ who may also be seeking ‘permanent employment’ or simply motivated by a day rate or extending their tenure.