Depends on coral, IMHE.
Candycanes, hammers and frogspawn had no problem with white xenia, gsp,
hairy mushroom and plain red mushrooms, non-photosynthetic softies, in a tank with no skimmer and rarely carbon. SPS porires, elkhorn and birdsnest did well togeter with them too, same conditions, plus additional yellow polyps, blastomussa merletti and lobophillia - trouble free.
On the other side, the large single open brain type corals - scolymia, cynarina and Symphyllia valenciennesi - did much better in a separate container.
And more of this, my cynarina doesn't like to have scolymia in proximity, especially upflow - and both are LPS.
I don't appreciate hammers, drogspawn and the candycanes with massive skeleton - they have a long enough sweeping tentacles, to place the neigbours in danger.
GARF is using xenia bed as a refugium for the nutrients export for their sps tank, with
protein skimmer, though.