I've heard a lot of recommendations to use the KOMA-Script document classes in place of the base document classes. I appreciate that there is a lot of added functionality, and customisation is easier. But before I jump in, I would like to know of any potential problems with these classes.
In my particular case, I am writing a thesis - it's part of the way through, and I've been compiling using the base classes (report), and a bunch of packages. But in the interest of keeping the question broadly relevant, answers with problems that don't affect my use-case are more than welcome.

