The dog bones take up slack in the system, but not I'd suggest wear in the drum face. What they do moreover is change the alignment of the shoe inside the drum. This has all been explained before but in short, once any part of the show hits the drum, it feels like the brake is on. Well it it, but with only a tiny part of the show making contact. If you drove for 100 miles with the handbrake on, it would eventually machine the shoe to touch all of the drum. But then it would also be knackered. The longer bone re positions the shoe so that more of the friction lining touched the inside of the drum to begin with. Now quite whay all of this is necessary is one of those camp fire debates I'm afraid.