In the old days of floating logs down rivers, there were times when the log raft would get all jammed up and unable to move. Into this uncertain situation came a fellow called a jamcracker. The jamcracker's job was to look over the log jam and find the points that, if changed, would break up the jam and let the logs flow freely. The job was extremely dangerous and the jamcracker frequently used dynamite to do the job. This is not unlike the situation found in a modern shared service groups.
Organizations have a love/hate relationship with their shared service groups. For a shared services group to benefit the larger organization it must provide quality service to other divisions. When that fails to happen, managers in those other divisions will do anything they have to do to accomplish their mission, even if that means by-passing the organization that should be providing them services. Efforts to force its use "for efficiency's sake" will be met with resistance, hostility, and a lot of complaining.
At this point, the shared service groups can take one of several routes. They can recognize their problem and correct it, or they can develop defensive mechanisms to cope with the onslaught of criticism and protect their jobs. The former is difficult to do and the latter reinforced by the lack of communication that ensues. Eventually both sides settle into a kind of unhappy truce.
Being the jamcracker in this stalemate is a dangerous proposition. Both sides have been entrenched for such a long time that it feels natural. Anyone attempting to change the status quo is likely to be caught in the cross fire as they are seen by both camps as somehow in league with the other. The solution calls for finesse, toughness, and an willingness to take risks. It also requires a hearty constitution that can handle the long hours that offer little appreciation and sometimes open hostility.
Jamcrackers work best when there are supporters all over the organization who can recognize where change is needed, help spread the message, and, occasionally, watch the Jamcracker's back during a particularly risky operation.