The "medicated" element is a coccidiostat, as the name suggests. You feed it to prevent coccidiosis from taking hold of your hatchlings, which are VERY susceptible to it.
Coccidiosis is a parasitic disease, caused by an intestinal fluke. This critter can live for a long time away from it's preferred host and is harbored in droppings and damp spots around the chicken yard. It is one of the top chicken diseases and all chickens are susceptible to it. Naturally, chickies are especially liable to pick it up.
It's root cause is overcrowding - too many birds in too small an area.
This is a prime reason why you should play it safe with chickens:
Moderate their numbers, do not put chickens on land that has previouly housed them in confinement for 1 or 2 years, and rotate your own confinement reared birds to new living areas every year or so.