Increased client satisfaction. Fewer defects mean that the client will be        more satisfied. Higher service quality will also make the client experience much more pleasant. If you are in a “for-profit” business, this will result in goodwill and may translate into additional sales, or higher margins on future products.

Higher productivity. Fixing errors and reworking previously-completed deliverables are a drain on productivity. In fact, they contribute to negative productivity. If the deliverables are produced with higher quality and less rework, the overall project productivity will go up.
Lower costs / shorter duration. Although there is an initial higher cost to a quality process, this is more than made up with less rework toward the end of the project. This will save time and cost on the project.

Higher project team morale. Team morale suffers if there are many errors uncovered during the project. People feel bad when errors are uncovered and it can be frustrating to have to correct errors repeatedly. Team morale will rise (or at least hold steady) if deliverables are created with fewer errors the first time.

Fewer errors / defects. Higher quality shows up over the life of the solution with fewer defects and errors. If you are producing a product for sale in the marketplace, higher quality means fewer returns, less warranty work, fewer repairs, etc. If you are creating a long-term solution, this means less support and maintenance problems over the life cycle.