A bank I am coaching has a team using Scrum. They are focused on delivering security related features to protect the bank from external and internal threats. This non-software based Scrum team struggled for several Sprints on the idea of value. The specifically struggled with how to break up large pieces of work into small pieces of value. In many Sprint Reviews there was a heavy focus on showing progress on uncomplete work to get credit for their efforts rather than showing small pieces of completed, valuable output.
Often, the team had an excessive amount of work in flight and at the end of the Sprint, when little was done, they struggled to understand why. To teach agile concepts, I often use cookie production as an easy to digest (no pun intended) way of communicating value, throughput, WIP, inventory, flow, and small batches. I especially like to talk about cookies being of value to a customer and raw dough being of zero value until its finished as a baked, chocolate chip cookie. I used this example consistently with the Security Team and the benefits have finally paid off. They are now to the point where they talk about the backlog items in the Daily Scrum as being ‘cookies’. Everything they deliver is now a cookie! In the Sprint Reviews they playfully call each request a cookie and use a slide of Cookie Monster to push that humor over the top.
Making a long story short, they now really understand the value of thin slicing the work and delivering value every Sprint.
Do you have any good examples of metaphors that really worked for you?
The Gospel According to Robb 
Why did you choose cookie as a metaphor?
I often use cookies as a metaphor. 1) cookies have no value to anyone until they are finished (mixed, baked, cooled). 2) if you have never made meatloaf spinach cookies before, best to make a small batch and see if you can sell them before making a truck full. 3) Everyone loves cookies, so its a simple and playful way to describe measuring delivery of finished product (rather than just progress toward completion of a large batch), the benefits of small batches in uncertain environments… and for those using Kanban, what better defined process to use for an example than cookie production!
True. But I guess any kind of product does not have any value until they are really done. What makes cookies different to any other product then?
Cookies are a product to which many can relate. They are simple. I Like using a simple and common language whenever possible to describe concepts that get lost in the complexity of the domain at hand.