Well people usually use live rock because it cycles the tank faster, because it can have some cool hitch-hikers, and brings in lots of good algae and stuff.
The way I see it: it was ripped out of the ocean and then exposed to air, then shipped with little or no water, which is at least a week: during this time most organisms died. Then it is taken to lfs, cured, etc. some of the things revive and most dont - rather it is the organisms from the lfs that end up colonizing the rock. Then once again the rock and organisms is shocked being brought into your tank. Then you can bring in unwanted hitch-hikers.
Some people like surprises, I dont. I like to know exactly what goes in my tank and why. Call me no fun but I would have a heart attack if I were to find something unexpected: good or bad.
Furthermore, I have cycled my tank already and I do not care about waiting for the process - I am in no hurry. I have my nice dried-out dead once-living coral skeletons and they make me happy knowing nothing is in there that I may not know about. I work in a lfs and know all the things that can live in there and it terrifies me.