When speaking about history as an academic field, the great benefit of revisionism is actually its disruptive effect on academia itself. Like any other field of study, history has its dogmas and calcified traditions. Revisionist interpretations, then, have the advantage of challenging those older traditions and introducing new problems, interpretations, and methodologies for consideration. They can even, in some cases, overturn that older established narrative entirely, bringing about a new standard narrative in the discourse.
However, your particular question has a narrower focus, given that it is centered upon historical individuals (and the so-called "great figures" approach to history). In this case, I would note that "great figures" history tends to involves hero worship by its very nature, and a revisionist account would, at the very least, moderate some of that hero worship. Historical figures were still human beings, the with flaws and failings this involves. Furthermore, in celebrating these individuals and framing them through a heroic lens, we risk erasing the unpleasant side of historical reality, one which can often contain atrocities.
That being said, this kind of revisionism can be manipulative in its own way with the historical record. This is especially the case if you are focusing your analysis on the personal faults and flaws of historical figures. Just as people are usually too complicated to be judged solely by their virtues, the same logic will often apply to their failings.
Furthermore, there is the problem of anachronism: if we are interested in trying to understand the past, we need to recognize the degree to which human cultures and societies have changed and transformed over time. While historians should be interested in testing and challenging these "Great Man" narratives, they should also be careful not to risk creating a counter-myth in response.