French term (edited): r�fection tablettage g�noise

I think you'll find that – in times gone by, at least - they cantilevered more layers of tiles out from the wall as the building gets higher simply because the building gets higher and, accordingly, the height of wall exposed to the elements (sun, rain) is greater, so you want or need eaves projecting further beyond the wall. One layer of cantilvered tiles serving as - or as a structural support for - the projecting eaves will extend the roof a few inches. Having a second layer of tiles cantilevered beyond the first will extend it a few more inches, etc. However, if you want your eaves to project a long distance, you cannot simply cumulate layer upon layer, extending a few inches every time, since there will come a time when the structure simply isn't strong (=deep, basically) enough to support the weight. This problem can be overcome by diminishing the cantilever distance of each layer, i.e. by having TWO (or more) layers of tiles instead of one to achieve a given incremental overhang, thereby resulting in an even greater number of courses at height. The end result of all this is indeed a very decorative effect, but basically for structural reasons. Of course modern buildings will be made with modern materials, with roof overhangs achieved with steel beams or concrete dissimulated behind "fake" tiles tacked on (until the mortar fails and they fall off), so indeed, in your builders' minds they will be decorative. Same principle as the moulded "masonry" gate post units, brick walling panels, etc. one can buy in any DIY store.