Like it says on the tin. Suppose that particular type of weapon had never been developed. Would there be different outcomes for the wars in which they were used IOTL? At the very least I'd imagine a higher body count, since more soldiers and civilians would be getting killed, instead of just rendered emotionally or epistemologically incapacitated for a limited period of time.
I read an interview with Dr. Leary, a psychologist who played a key role in developing the USA's arsenal. He said that before he went to work at DuPont, he had had a midlife crisis in which he seriously considered becoming a beatnik and taking LSD for the rest of his life.