Gold plating is the addition of features in a project that were not requested within the Project Scope. Project Scope Creep comes from the customer side, where as Gold Plating is introduced by the Project Team. Gold plating can be a good or a bad thing for a project, as the customer may or may not accept the change.
If the customer accepts the change, all is good, except that this may have cost the project some time or money. If the customer does not accept the Gold Plating, then remediation work may have to take place to back out the changes to the original scope, which will potentially cost both time and money.
As a developer, Gold Plating used to be an easy trap to fall into. I would often add additional features and functions to software packages that I would write, which would normally be accepted by the customer. However, on a rare occasion, the misinterpreted understanding from a developer does not coincide with the thinking of the users and changes that I had made needed to be removed, at a cost to the project.
The project Scope, Schedule, Costs, Time, Quality and Risk are all inter-related; If you change one, you affect the others. By Gold Plating you are actually increasing the Scope of the project and this will have an impact to the Time, Costs, Risks and Quality of the deliverables in one way or another.
As a Project Manager, I ensure that I control both the Scope Creep and the Gold Plating in the same way. I ensure that I confirm and agree the Project Scope with the Project Sponsor at the beginning of the project and stick to it. As the project progresses, I ensure that we stick with the original scope and that we do not deviate from the plan. Obviously, Change Control can play a part in modifying the scope, but this must be controlled.
It is not the role of the Project Manager to exceed the customers expectations, but it is their role to deliver the expected deliverables. Nothing More, Nothing Less.