I've owned one for about 3 years before I had to remove him/her. Great fish, fun to watch, and did remove all of my aiptasia. My 40 breeder is mostly soft coral with the only LPS being hammers. I also have 5 rose bubble tip anemone's.
Soft coral mix is green star polyps, green buttons, some zoas, kenya tree, xenia, golden leather, finger coral, and I think that is about it. Of those corals most of them are very established especially the hammers. Started with one small frag and they are softball sized - all 4 of them. The matted file fish did clear out my zoas - not that I had many to begin with but I'm pretty sure he got them. I saw it pick at the hammers and kenya tree but never was able to hurt them. They grew faster or he didn't much on them much - hard to say but I'd see him do it.
Funny thing is I put in a xenia frag and in about two days he went for it. That is why I caught him and returned it for credit. The xenia was small and couldn't keep up with the constant picking so I chose it - I know, most people would have kept the fish. However, I just wanted it to get a bit more established then I wouldn't care.
Short answer is mine cleared out the pest, picked at my LPS (hammer) and more than likely ate my zoa's (brown color, nothing fancy). Other than that great fish, very peaceful, and excellent personality. Ate pellets, mysis, brine, flake, and nori. All around easy fish to keep.