Can't answer for everyone, but I like live rock (and have paid loads of bucks hand picking it up here to prove it!) because I want my reef tanks to look like wild reefs, or as close to it as I can accomplish with my measly reefing skills.
Plus, I like the life that eventually emerges from the LR - different kinds of sponges, some really nice ornamental macroalgae, pods that scurry over the place, fan worms - so many lovely additions to my tanks
However, I could do without aptasia (spotted a new one this morning that I have to vinegarize), that awful worm that slimed and killed my snails, and those dark, hairy crabs that I'm sure are up to no good
But the biggest advantage to LR is the many, many, MANY freaking ways it can be stacked into different aquascape designs
LR has given me so many options in setting up my tank (not to mention backaches, headaches skin abrasions and a bit of a rash now and then) that when I get tired of one design, I just go back in in several months to improve the design flaws from my last attempt
