Questions about preferred methods of achieving an effect or other result. Using best practices may affect, amongst others, compatibility, degradation, and usability.
Wikipedia defines 'best practice' as:
A best practice is a method or technique that has been generally accepted as superior to any alternatives because it produces results that are superior to those achieved by other means or because it has become a standard way of doing things.
So, best practices aren't the law!
In graphic design, best practice might refer to a design technique, or to an aspect of a design business.