They don't amount to much in home aquariums. They are also referred to as strawberry anemone or ball anemone. They don't get much bigger than you have them. Perhaps the diameter of a dime at best. No, they won't cause any issues for anything. They don't spread to biblical proportions, or sting everything to death...you'll see them from time to time but for some reason they don't last very long.
Folks get these confused with Pseudocorynactis, which look similar, get pretty big, and have the ability to eat fish. I assure you, this is not what you have there.