What exactly are you talking about? Do you mean the little plastic piece above the blades on some of the popular small Andes clippers (and maybe others)? Those get bumped a few times and the plastic clips get broken or bent to where they just don’t stay on. So most of them either get trashed or are randomly floating around in a clipper box/bag.
Or do you actually mean the guards of various thickness that you snap on the bottom of (some) blades to keep you from taking off too much hair? If that’s what you mean, you simply can’t blend and shape with those. They work only where you want to leave everything the same length in relation to the body shape underneath it. About the only place you ever see anyone use them clipping show cattle is maybe on the sides of the neck, and at that it’s probably only because the calf won’t hold still enough to let someone block it in correctly.