It depends. Corals compete for space. Soft corals generally use chemical warfare to deal with rivals. So if you want a bunch in your reef, you might want to keep on top of water changes are regularly run charcoal.
LPS corals tend to use stings to deal with their neighbors so you want to have a buffer between them and potential victims.
SPS corals are the wimps of the reef. But montipora corals grow fast and can sort of grow over and cover up other SPS corals. They can’t do this very well with LPS corals.
Acropora corals with their more vertical approach can actually shade out montipora. But usually montipora can grow over them before this happens.
So to keep the reef balanced you sort of have to do trimming to keep the more aggressive stuff in check.