Change is a Political and Behavioural process and a specialist change agent can often achieve a great deal more than an internal practitioner
Externals can confront the politics of change, power plays and deal with resistance head on if required
External OD people usually have a behavioural background, grounded in business in a variety of industries - and are experts in change management and probably author reports, and articles which reflect best practise. They are paid professionals who should be ahead of their field
Externals don't have to worry about their career in the clients business because they don't have one. They are not concerned about their continued progression up the organisational hierarchy as do internal change agents. Once the project is over they can move on
There are always winners and losers in the process of change - that is reality. Externals learn and move on and ensure that they leave a contented organisation behind them. Internal change agents have to live with the some of the unpleasant consequences of their interventions and the decisions which have been implemented
Introducing change is often seen as a threat rather than an opportunity. External change agents can be more objective and will be prepared to speak up and take thoughtful risks
Externals by their very nature are highly experienced at working across a range of industries and sectors. They will have come across difficult problems before and have more experience and tools at hand to manage the change
Externals reputations determine whether they remain in business or not. Experienced change agents will always have lots of business and a huge network of trusted associates
It is in the interests of the external to delight her or his customers. If change agents don't achieve their standards upon which they are employed there is a likelihood they will not be paid for their intervention and their reputation in the market place will die.