It's potassium iodide (KI) and it's for protecting the thyroid gland from developing cancer later and the younger you are the more you are at risk. (if you have young children for exemple you should consider it more seriously than if you are 40 and over and live alone)

It must be taken shortly after the exposition, something like within 4 hours and it only protects against radioactive iodine and it's not always the isotope used in every nuclear emergencies. It would be unlikely in a dirty bomb and maybe if you live near a nuclear plant you should contact the plant directly to know about emergency procedures. Besides there is also a risk of allergic reaction.

As for me, I won't bother with rotating pills as I do with other medications like Imodium or Benadryl since I guess I'm not at risk.

Frankie