Who does it? It seems heavy SPS tanks somewhat stay SPS tanks. I'm looking to stay as a mixed reef with a decent amount of LPS but mostly SPS. I would like to know the advantages/disadvantages of keeping everyone happy. I see in the by sell section people sell off corals because they are going "dominant SPS" To me if you have the room why not keep them? Sorry of this is a repeat or completely noob question.
Look up a few corals you are interested in on the "Corals of the World" website and see what their habitat is in the wild.
There are lots of corals that are found "everywhere". You may find keeping these types together to be the easiest.
There are also plenty of corals that are found in "peculiar" environments, such as "deep water", "shallow water", "lagoons", etc....these corals may carry more requirements or have different requirements from the "everywhere" corals, so more research is very often recommended and keeping them out of a mixed reef would be a good default position.
How's that for a generic answer!?!?!?
Here's the website I mentioned:
http://coral.aims.gov.au/info/search.jsp