Throughout my career I have always believed in the use of consultants to add expertise and to provide a different point of view on difficult issues. I do not think that consultants should be use to shift the burden of decisions to take action. The company always must own the decisions it makes and not say "we were only doing what the experts told us."
One example of the use of consultants was for public relations. We had lots of ideas on what to do but needed someone with experience in our business sector to provide options for us. Choosing an image package was one big issue. Our PR consultant gave us lots of ideas and alternatives and we selected and implemented.
Another use of consultants is to augment your internal resources to move more quickly. By managing the consultant carefully is essential, use their strengths and fill in where they are weak. When we were redesigning our office space an architect provide awesome alternatives. However the implementation really dragged on and we realized that they were overseeing the project as opposed to managing the contractor. We quickly took over management and got the project finished quickly.
In providing assistance to our clients, we are very careful to make sure the client understand the division of responsibilities. Every project requires cooperation between all the parties involved. Communication, mutual respect, and trust are the cornerstones of good cooperation. When an issue is identified, mutual problem solving is important. Finger pointing never solved an issue.