Maybe not that often but I think it's a nice thing to have, especially when setting up new cables. I guess it's a personal thing. If you drill a larger hole and fill it with an aluminium bolt the weight should stay about the same. If you still have the head on that M8 bolt it'll even go down. As said the nice thing about the sram derailleurs is the cable guide in the arm as it doesn't really matter how you position the cable, it'll always pull in the right direction. If you try to do the same with a DA derailleur (take out that little steel ring that keeps the cable from eating it's way into the aluminium f.i.) it won't shift as well.