Maybe you don't understand it, but that doesn't mean you don't rely on it. If I said an OS was unusable by 99% of people because it didn't support multithreading, it doesn't matter if 99% of people know what multithreading is, that's clearly a true statement. Similarly, if you've ever expected your PC to have the same files on it tomorrow that you put on it today, then you might find it annoying when that's not the case.