In my profession, I have been involved in many of these types of projects. Some have worked very well and resulted in very significant savings for the companies involved. Some have not and the savings realized were very small. In the cases where it worked, it was part of a top down driven plan to reduce overall costs and increase productivity. By top down, I mean that it was part of an overall plan that was driven by upper management and instilled into the culture of the company through total employee involvement including education on the benefits to the company of each employee's contribution to reducing costs, inclusion of specific goals in each employee's performance objectives and incentives where appropriate. Each followed a well thought out and documented plan that included a cost/savings/productivity analysis by location that was developed with the total involvement of each location's management as well as corporate managers. Vendor selection was also a key area that was addressed by once again involving the local management in developing the metrics to be used in evaluating potential suppliers. Several layers of management and employees were involved in the evaluation process to offset any "favorite son" bias that may have existed. Another key component is the ongoing measurements that are reviewed monthly or quarterly to insure that the objectives continue to be met or necessary adjustments made.
Where this kind of road map was followed, the success rate is extremely high. Where it was a mandate that was forced by corporate with little or no involvement of the individual locations or employees, the success rate was low. Where it did work, I have seen average savings between 17 to 22% with some saving as much as almost 30%.
Hope this helps.