As guy said you would not want a fish whos natural diet consists of the exact same corals and sponges you have spent money on and are trying ot keep.
Some fish species are
as to if they will cause a problem. Like the pigmy angles. Some may and some may not go after the sponges or soft tissue corals. Others might not at first but might develop a taste for them later on.
And dont worry about asking questions. If you dont ask you wont learn. Not learning is a bad way to go about life. Personally I enjoy learning so that I can then turn around and shaire what I learned with others. Thats the entire purpose of this site. To share or experences and knowledge with others and at the same time forming a community of people with common interest.
The ONLY stuipid question to ask on this site is the one that never gets asked.
p.s. I give you kudos points for asking such a good question.