Nothing really. It’s a myth. Easy sps are easy. A two inch frag if montiproa won't
do much to a 30 gal tank as far as alk and calcium goes.
We’re not jumping strait into acropora.
But you will have to watch it and keep up on water changes when it’s six or ten inches you’ll just have to to more wc or decide to dose. I grew montis and stylo and other birds nest years before I began dosing.
When folks refer to easy coral , they refer to its ability to survive the minor swings and nutrient levels. This simply isn’t true of many “softies” folks default to.
I have a branching monti right now that would grow in a swamp I think. And I recall some leathers I’ve killed while my Hollywood stunner chalice just got way too big. (It has sweepers)
Whatever magical chemistry thing that happens in a tank that makes it “like them” is different. This goes from sps to Xenia. So tester corals are IMO important. It’s also an opportunity for the reefer to learn about them and experiment. Flow , placement , light etc.