others have articulated it much better but I think the difference isn't in what it can do. But working with existing docs - subtle things like font differences, formatting issues, working with the rest of the world that is MS dominated, keyboard shortcuts for excel warriers. LibreOffice is very capable on it's own, as a drop-in replacement is where it doesn't work most of the time. And the difference isn't even huge, but people being people give up fast.