There are, as you know, a number of mooring buoys at Monad but boats have still been known to use anchors - but there are plenty of times where there are more boats at the location than there are buoys...
In the case that I watched, though, the anchors were being used IN ADDITION to a mooring buoy as a way to stabilize the movement of the boat in big swell. I don't know if the anchors were even touching the substrate - either way its bad for divers who are in the water as the anchors are being dropped and then of course bad for the substrate if the anchors touch it at any point.
Check out this video if you want to see flagrant use of anchors at Monad. I can't believe this guy Jonathan Bird gets paid for what he does - he is such a nitwit. He makes it seem like Monad is the wild west and that you can't just motor 20 metres away and pick up a buoy.
YouTube - Jonathan Bird's Blue World #6: Thresher Sharks. Its people like this who give diving and underwater photography / cinematography a bad name.