There's a lot of explanation here but ultimately this is basically just the standard 16-tile set except assuming you can use rotations to deduplicate and don't need to allocate a tile for empty space. The latter makes sense for platformers (since your tiles likely represent objects that are supposed to be floating over some other background drawn another way) but not so much for, say, RPGs. (And the rotated tiles are often not great in RPGs, either.)