Exactly. It's all about logic. They other types of bugs are caught by the IDE, the compiler or the first run anyway. Let someone else look over your code, they

Exactly. It's all about logic. They other types of bugs are caught by the IDE, the compiler or the first run anyway. Let someone else look over your code, they might spot logic bugs that you oversee. If you write tests yourself, you will often oversee such logical bugs. I have done (semi-)automatic reasoning and code verification with 100% code coverage of OS drivers. All the mathematical reasoning doesn't spot logical errors. You need more than one person to look over it.