If it is a ball anemone and not a majano(tough to tell from your pic, but the little ball tips leads me to believe its a ball nem, and not a majano), I have never had one cause any sorts of problems. They tend to stick to area in low flow, and low light.
Also majano's grow, ball nems tend to stay on the small size. If it continues to grow, eradicate it. if it stays small, it's probably a ball nem.
Also majano's grow, ball nems tend to stay on the small size. If it continues to grow, eradicate it. if it stays small, it's probably a ball nem.