I just did the AMEB normal exams, but did know people who did the piano for leisure. The two main differences are the range of music you can play. Music for leisure has much, much more selections, thus you can find easy pieces if you want, rather than the rigours selection criteria for normal. And also, the technical part is easier in leisure, as there is not near the amount of scales and such there, and in high grade leisure, the keys for this technical work are equivalent to those of lower level normal.
So the titles pretty tell you the difference, the normal one is more technical and difficult, thus if you like challenges then this is godd, whereas leisure, is just that, but of course with a bit of difficulty, but not as much as the other one.