When building software, quality assessment is something that usually is pushed toward the end of the life cycle, just before the release. When the team is working in a 6-months release cycle, the drawbacks are not as obvious as when the release cycle is just a few days old (or even hours!), but from my experience, I can tell you that getting early feedback in your software is crucial in order to raise the quality to a good level we are comfortable to live with.
There is a misconception in the software that puts the average software project in danger: the software has to be perfect. This is totally incorrect. Think about some of these real-world systems: the engine of your car, a nuclear plant, the water purification system in major cities, and so on; human lives depend upon all of them and they fail. A fair amount of money is spent on these systems without...