There are estimates that somewhere between 40% to as much as 80% of the lifetime cost of a software is spend on maintenance.
Throughout the software lifetime, maintenance will be conducted by different developers, and even for the original author of a particular piece of source code, after a long period, it can become difficult to remember the rationale behind it.
Consistent use of coding standards, such as naming conventions, indent style conventions, line length conventions, etc. improves readability and drastically reduces the time it takes to understand the software source code.
Another benefit from adopting coding standards is reducing overall complexity by suggesting a maximum line quantity for methods or functions, resulting in smaller, more specialized and easier to understand source code.
A source code that is easier to understand will also help defect detection, improving the overall software quality.