From a liberal perspective it’s very useful.

-Because Hitler alone was responsible for WWII you avoid having to deal with the fact that a huge part of the European population were (and still are) rabid fascist freaks with a taste for genocide.

-No ordinary people in any country ever actually wanted a socialist revolution, they were all forced on them by people like Lenin, Mao, and Fidel, who were of course exactly the same (or actually worse, because reasons) as Hitler.

And so on.