I don't honestly know why most people do code reviews, because it's often presented as some kind of "quick sanity check" or "plz approve". Here's why we do code reviews where I get to lead the practice:

1. Collaborate asynchronously on architectural approach: (simplify, avoid wheel reinvention)

2. Ask "why" questions, document answers in commits and/or comments to increase understanding

3. Share knowledge

4. Bonus: find issues/errors

There are other benefits, like building rapport, getting some recognition for especially great code.

To me code reviews are supposed to be a calm process that takes time, not a hurdle to quickly kick out of the way. Many disagree with me however, but I'm not sure what the alternative is.

Edit: people tend to say reviews are for "bug finding" and "verifying requirements". I think that's at best a bonus side effect, that's too much to ask a person merely reading the code. In my case, code reviews don't go beyond reading the code (albeit deeply, carefully). We do however have QA that is more suited for verifying overall functionality.