It's less about the amount and more about the correct variety. Variety can be good, but it can also cause problems through coral warfare. Also remember, pruning is a very important part of coral maintenance in any reef aquarium. If cared for properly, any coral will outgrow a typical aquarium, and pruning is necessary. So, what I'm saying is, you can have one coral in your aquarium and have it be overcrowded.
Interesting that you put this query in the LPS Section.
With the LPS corals you have to be wary of the sweeper tentacles.
With SPS you can pack them in and they will grow into, grow around, and grow over each other.
When mixing LPS and SPS it depends which you want to win the battle. LPS usually win by taking out the SPS. But in the long haul, the SPS can grow over the top and block the light.
So... tell us what you are planning or plotting for and perhaps we can give a better answer.