To me the only coral that is a "pest" is STAR POLYPS! They grow like WEEDS, and when they spread too far, it's difficult to "Trim" them back, You can't just peel them off the rock, it rips in tiny pieces. 1/2 my tank is Star polyps now and the only way I was able to controll them was to put an Anenome on each size of them, I call it "Natural" weed controll. The Anenome's happily sting the ends of the Star Polyps and keep them from spreading any more!
As for Xenia's They grow pretty fast in my system (I have a very clean tank, I have NEVER had Nitrates, Nitrites, Ammonia, Phosphate, etc. But they love my tank. If/when they grow/spread too far, I just pluck them off the rock and either throw them out, or sell them to the LFS
. They come right off the rock, so no biggie.