If it means European toilet paper size, then I think it's a convenience, because it happens to be a nice fraction of the standard A-type size paper you get over here
EDIT:
In fact, toilet paper in some European countries is A6 size, which is exactly one quarter of a sheet of A4 paper, which is a standard paper size outside of that weird place called United States

Would be useful if you wanted to print the same thing 4 times on a sheet of A4, for example
