I have only seen a few ladies that list that as something they do. Those that do seem to speak highly of it as something they enjoy, and I have also read reviews where one finger inserted leads to another and then another and the reviewer describes it as fisting,  

What seems so odd is that many seem to react negatively to it like it is a bad thing,,, Which seems odd. If the lady enjoys it and does it or she does not and chooses not to do it I am not sure why it is something people seem to judge in a negative light.