I had something more in mind like the Doom 3 mtr for example, each image can be use to combine with others to overlap and create certain effects.
EX. _s in doom is for spec _local is for normal mapping _d is for diffuse and _a is for alpha I think, height maps can also be use for z depht.
So if I had more then one diffuse image that I want them all to use the same alpha then this will required less work and less hard drive space.
Look here for more info on doom 3 texture http://www.iddevnet.com/doom3/