Software is create by humans. It's inevitable, then, that it will contain some defects or errors.
Rather than putting all of the pressure on the testing teams to investigate and find as many bugs as they can, many developers and development managers reap the benefits of finding defects early in the process via peer code review.
The infographic below covers the basics of what peer code review is, how it has evolved over the years, and gives some tangible statistics that may help you be more efficient in your code reviews moving forward.
(Click image to enlarge)