Whataboutism, also known as whataboutery, is a variant of the tu quoque logical fallacy that attempts to discredit an opponent's position by charging them with hypocrisy without directly refuting or disproving their argument.
It is important to know whether the condemning party applies the same standards to their own activities, because there's no possibility of resolving the issue at hand without both parties applying the same principles and standards on everyone, including themselves. And dismissing the significance of this knowledge as "whataboutism" is short-sighted, because it's the tool of establishing standards of morality, and it gives a hint to third parties about the nature of their neighbours involved in the dispute.
In practice it means that the side who accuses first (currently mostly SJWs) gets to speak and attack others while using "whataboutism" as a shield to shut up their opponents.