Some people pay money for mushrooms,
Problem is they get huge in my tank (3 inches across) and they kill anything they touch
Can't cut them off the rock because they leave a little bit of flesh behind and that will grow into a number of new mushrooms.
I would personally never add these to any tank with SPS again. Great corals for a low tech tank though, I've got some growing really well in an unheated goldfish bowl on my windowsill.