A good code review process can greatly improve code quality while bringing significant benefits in engineering team culture.
At its most basic, code review helps catch errors that would otherwise have been missed by the author of a code change. Involving more senior engineers and/or those with more experience in a particular codebase or technique can catch higher level issues such as leaky abstractions, locking hierarchy or threading problems.
But just as importantly, code review can be used to encourage engineers to take responsibility for their work. Not just make something work, but think through what they’re doing, understand it, make a good change, and be prepared to defend it.
A team that can respectfully give feedback and even challenge each others work is a stronger team.