Change control management or scope control management is vital to project success. If you have worked in project for more than 5 minutes you would have heard the term scope creep.
Scope creep can be like kryptonite to a good project so it is vital to have an effective, communicated and controlled project change control process in place.
Everyone must be made aware of this process and it must be enforced and adhered to, there should be no exceptions because a couple of little exceptions become one large on, and one large cost and addition to project duration.
It also runs the risk of allowing items to be included in the project without the appropriate impact assessment being carried out on them.