I recently sat in a meeting between a vendor and client, where the client was attempting to communicate their need to route new work deliverables to an existing Change Control Board (CCB). The contractor came back and said they believed the CCB in this case would not provide value and perhaps it should be bypassed.
Note to all vendors: Just because a process does not appear valuable to you, it does not mean the process does not provide value. The use of the CCB provides a (formal) control point helping to prevent unauthorized work and cost overruns. This goes further then just having a client billed for unauthorized work. Any work done without prior authorization has a risk of negatively impacting project schedule, cost, or quality. The mere act of doing unauthorized work impacts the scope.
I don't care if you're using Agile, Waterfall, or other methods to deliver value. What is important is you understand your process and what mechanisms provide the greatest value to the customer.
If you think you need to deviate from a documented or understood process, rewrite your process to account for the deviations. If you are unwilling to change your documented process, the deviation is unworthy of being done.
I created the Visio diagram (above) a few months back to help both the customer and vendor visualize what we were trying to accomplish. The challenge was implementing Scrum in a very formal and controlled environment.
I certainly recognize many don't have such a formal process. Instead of CCBs, you may call them Product Backlog Review Meetings. Counter to this, you may have a very fluid and simple software development life cycle (SDLC). If so, you still need to understand your process and you still need to communicate with your customer. Understand what their highest priorities are and deliver.