There are some case where you want a user to be limited in what he can do. For example, let's say that you are building an X terminal server under Linux for a primary school (in my case, Institution Ste Clotilde, Strasbourg). In that case, it is mandatory that the system can be used by people who aren't very familiar with computers.
Though KDE is simple and comfortable to use, it can't be used this way in a primary school. The main advantage with KDE may also be a problem in our case. Thanks to KDE, everything is simpler for a pupil, including inconfiguring one's desktop in less than two minutes (some people rather speak about personnalization, but that's another point), and once your desktop is in a mess, you may ignore how to recover your original settings. With KDE, you may :
change the background settings ;
change the screen saver ;
change the desktop theme ;
browse Linux's system directories with Konqueror ;
perform actions which are supposed to frighten the teachers, and people who don't feel at ease with technical questions.
To sum up, what shall find something that would reassure the teachers. And how could you be more reassured than if you knew that your desktop settings are refreshed each time you log in, so that you just have to logout and login your original desktop ?