Normally areas of wharves, marinas and tends to be more shallow depth. It can also be in areas with abundant life like Indonesia, where the small critters are amongst spectacular soft corals.
Muck divers tend to be slow patient divers who are looking for rare nudibranchs, juvenile fish, frogfish and small, strange critters not found anywhere else. Match this and a camera, with a Macro Lens ( hence the name), the diver can get close and detailed.
Which means awesome underwater photography!