The last letter "M" in the popular abbreviation «EPCM» means - Management
Quite often, this function is taken over by the Management of the Customer or separate Customer Structures which created for the implementation of a important and major Projects.
It all depends on the scale of the Project and the availability of qualified Managers in the Customer's staff in the number necessary for successful management and implementation of the Project.
A variety of combinations of Customer and Contractor structures are possible, with a variety of tasks, functions, duties and responsibilities.
If there are many managers, the only danger that occurs is the "Rob Peter to pay Paul" syndrome. When it seems like the buttons are firmly sewn, and the sleeves too ..., but "the Caftan does not fits well» :|
If a Project is managed by one strong, close-knit Team of high-class Specialists with a responsible Manager, there will always be a "tailor" who can "answer for a caftan".
The Master and his Team can be either rewarded or punished for hack work.