This article is part of a series on Scrum Primer. See the first post on Sprints
The Product Backlog is a laundry list of prioritised requirements from the Product's Roadmap. The Product Backlog Refinement activity involves adding, removing or even updating this list on description, priority, estimates etc.
here are three stages when this activity is required;
"How do we begin" stage - When the team doesn't have a Backlog yet
"New requirement in" stage - When the team needs to understand how to implement a new feature
"Keep it healthy" stage - Ensure the Backlog is up-to-date.
The refinement is about how you are taking in new requirements for the team to work on. The activity should certainly NOT be used for last-minute scope creeps because the "boss" said to add it. The Product Owner should carefully consider each change and manage it well. While you certainly don't need a whole change request committee, you can set some rules to test the change.
"The refinement process is always the biggest challenge for companies where I worked as a coach or Scrum Master and so often underestimated. I think it's the biggest flaw in Agile Scrum." Lieuwe van Brug, co-founder of Frontall.io and Agile coach