Muck dive sites are normally areas of wharves, marinas and tend to be at a more shallower depth, with black sand. Macro diving can be on coral reefs as well. It is these muck diving destinations, like Lembeh Straits, Mabul & Kapalai, that offer weird and wonderful marine life.
Muck divers tend to be a slow & patient underwater photographer, who are looking for rare nudibranchs, mantis shrimp, mimic octopus, juvenile fish, frogfish & small muck critters, like pygmy seahorses or ghost pipefish. Match this and a camera, with a Macro Lens ( hence the name), the diver can get close and detailed.
Which means awesome underwater photography!