I know I am Not speckled hen, so My views are a little different. I worm my flock every six months. This is because my birds are around alot of other peoples birds (Shows) and natural worms (live on a lake;herons geese and ducks always flying overhead and pooping). If you ever see a worm in poo, that means there is a HUGE load of poo, and they have trouble absorbing nutrients and are weaker. Worming also causes some headaches. You can't eat the eggs for 2 weeks (?) after worming, so if you depend on those eggs and can be a hassle. I also think, though not proven, my rooster isn't fertile after being wormed. So it is personal, and it depends on how bio-secure your flock is and your uses and needs of the flock. Mine are ornamental, if they were meat birds or possibly egg birds off the ground, then i wouldnt.
I have never seen a worm, and I hope i never do.
Mark