Avoid leaving commented-out code in the codebase. Version control systems already track the history of changes, making commented-out code unnecessary. Removing unused commented code improves readability, reduces confusion, and keeps the codebase clean. Example of code to avoid: ```yaml builder-to-testers-map: ubuntu-20.04-x86_64: - ubuntu-16.04-x86_64 - ubuntu-18.04-x86_64 - ubuntu-20.04-x86_64 # windows-2012r2-i386: # - windows-2012r2-i386 ``` Instead, simply remove the commented lines completely. If the code needs to be referenced later, it can be found in the commit history.