The only way to ensure that you're developing the software that the customer expects is to keep release cycles as short as possible. Even though the release will be small it should still deliver business value to the customer. As part of release planning, the customer works with the development team to define user stories and the order of implementation.
Another benefit to small releases is that the development team can use each release as a checkpoint where they measure estimation accuracy. During the planning stage developers estimated user stories based on their expected throughput and difficulty. We can now compare planned to actual, using these lessons learned for the next iteration.
Small release cycles are workable because we are building the most important user stories first, and our automated environment makes frequent integration painless.
How the customer defines the release is covered in depth in Hour 8, but for now we know enough to understand the value of small releases in controlling and managing.