Yesterday, I posted a quick thought on code generation, and one of the statements I made is worth re-stating to stand on it's own.

In Agile/Lean software development, a single User Story is one piece flow when implemented via TDD, in a Workcell

In Lean Manufacturing, one piece flow is the idea that you do not produce anything in batches, but that you produce one product from start to finish per a customer's order. In Lean / Agile software development, this is analogous to an iteration with user stories. An iteration backlog is a customer order - a set of behaviors or features that are requested to be delivered in the current iteration. A user story is the single piece that we want to flow from beginning to end - from the start of coding all the way to acceptance via user testing.

In manufacturing, a Workcell is used to facilitate one piece flow through the manufacturing process. In software development, a Workcell is also used to facilitate the one piece flow. The Workcell may be 1 person, pair programming or a three person team. In order for it to truly be one piece flow, though, strict standards such as TDD and automated acceptance tests must be followed.

I'm not going to detail the benefits of one piece flow, here (not yet, anyway... another post for another time). I highly recommend that you read The Toyota Way and Lean Thinking for a good understanding of this concept and the benefits it provides.