"I want it just like that one but with these changes" instead of "Here are the complete plans for my house". Both will work, but in the former case we might say: "Let's bring the team in that built 'that' house".
What's in a Build
This leads us to a fundamental requirement. Although it matters less how you track a build (i.e. baseline + changes + options vs new baseline), it is crucial that you can look at two builds and ask: What new features are there? What problems were fixed? How does it differ from what the customer currently has? What level of retesting is necessary? The Sikorsky S-92 helicopter was grounded with a requirement to replace the titanium studs in the gear box mounting with steel studs. No new baseline has to be established to correct the hardware. But a new build definition is needed for new craft. It may be due to a new baseline definition, or to an revised build process that says apply the following changes to the existing baseline.
The important thing in any case is that we can ask: what's in this build that's not in that build. I like a CM tool where I can take the customer's current build and then compare it interactively to various candidate delivery builds, just by scrolling through the candidate build list and then zooming in on the differences list for details. If instead I have to commission a team to describe the differences between every two builds, I've got a working, but painfully slow process.
Comparing builds is not just necessary for releases. If a key feature is noticed to have stopped working and I know it was working a month ago, I want to trace the changes build by build to see what functionality potentially impacted the feature. The more easily I can do this, the better. Traceability and zoom-in are critical. Similarly, these features will come in handy if a customer notices that something has stopped working. The ability for an orgainization to respond the same day, as opposed to days or weeks down the road, will make the difference between a happy customer and one that might be ready to take you to court.
Your current build process may be far from ideal. But if you can describe where you'd ideally like it to be, you can get there. There are numerous tools to help. There's plenty of expertise available. The demand for quicker turn-around continues to grow, especially as competitive pressures continue to squeeze profits. Make sure your processes are moving to the next generation, and if they're already there, keep on moving.