Using a checklist will never guarantee with certainty whether or not a use is fair. It can, however, help you organize and, importantly, document your thinking. It's a great idea to utilize a fair use checklist whenever you are dealing with a tricky fair use situation. Take the time to document your thinking in case of a future challenge.
Fair use is the flexible and dynamic exception to copyright law that serves to balance the rights of creators with the public interest in using copyrighted works to advance education, to comment and criticize, and to make new creative content. This flexibility can be confusing because it is very rare to know with certainty that a use is fair - rather, only that it is more or less likely to be fair. The law does not give any clear answers regarding amounts we can use and know that we are "safe," however, understanding the purpose and function of fair use can help grow confidence in determining fair use.