2 different method/results I'm thinking of where it occludes:
a) anything behind it (saving render time instead of rendering the whole thing and doing it in composite with a matte layer) I know there's the 'make a surface shader object in foreground' option, but am hoping there is something better...
b) anything inside the occluding object (for example a giant cube to make a cross section of rendered geometry) Key point being you can animate it. I think you can do that with booleans keeping the history? (correct me if I'm wrong) but that isn't appropriate for animating a cross-section of multiple objects in a scene.