How did Sigmund Freud change the world?

Being a pioneer, he had a lot of ground to cover and missteps to make. Later psychologists ironed out some of his steps and clarified ideas, making psychology a purer science with less "guess-and-by-golly". By the mid-twentieth century, psychoanalysis and psychiatry were solidly reputable and recommendable. By 'certain topics', I suppose you may be referring to human sexuality. Freud seem to be overly concerned about this when there is so much more to wonder about. Spirituality and the nature of consciousness, to name two.