Saltwater Sponge Taking over Live Rock?

I have one piece of live rock that seems to have a fast growing type of sponge on it. It's about a 3 lbs rock and is more than half covered by this sponge. I am planning on making my tank into a reef tank, I might be getting my first coral today. Should I cut back the sponge on that one rock before it over takes some of my other rocks? I know even if I do it will probably grow back, but at least I could maybe keep trimming it back as it grows. Do sponges hurt corals at all? I'm still learning about Saltwater tanks. I probably have at least some kind of sponge on every piece of live rock I have (13 pieces, roughly 35 lbs of rock) in my 33 gallon tank, but they are all slow growing and don't look like they will be a problem, just that one piece of rock. So should I cut that sponge back or can I just leave it?