Agreed value vs stated value in plain English?

New to the collector insurance side. Can someone explain agreed value vs stated value simply, and why it matters at claim time?

Agreed value means you and the insurer settle on the number up front and that is what you are paid, minus deductible. Stated value can pay actual cash value if it is lower. Always go agreed value for collectibles.

This. Agreed value or do not bother, and get an appraisal to back the number.