Since every environment is different, any and all code should not be run in a production environment without your team or organization thoroughly testing first. We recommend the use of a test lab environment often referred to as development/staging instance of Sitecore.
The disclaimer is provided because someone somewhere will inevitably not follow this recommendation and in the event that they do hose their Sitecore environment, they have no one to blame but themselves.
All data and information provided in this book is for informational purposes only. Adam Najmanowicz, Michael West, and the SPE Team make no representations as to accuracy, completeness, currentness, suitability, or validity of any information in this book and will not be liable for any errors, omissions, or delays in this information or any losses, injuries, or damages arising from its display or use. All information found in this book are provided "as is" with no express or implied warranties.