YOUR PROCEDURE is as good as you can make it and you've implemented it so well that all know exactly what they have to do, and all have agreed to do it. You're done, right?
If you've done your job right in creating (or revising) the procedure and rolling it out, everyone will come in tomorrow and follow the new procedure. But what about next week? And what if you made a mistake, or the business changes, or there was some information that you didn't have, so that the procedure doesn't work as well as you expected? How will you even know, and how can you make a case to improve the process (again)?
That's why you need a control and monitoring plan, which describes how the process is measured, ...