Quote: This is only if you bring in started birds from someone/somewhere else. Baby chicks are pretty safe and are in a brooder for 6-8 weeks anyway and should be kept separate until they are somewhat the same size as the older ones, for the safety of the young ones at integration. Ones you hatch aren't going to pick up anything and carry it to your flock. So no worries there.
Quarantining is for the safety of your flock, and so you can treat the new birds before integrating if neccassary. I have heard if you bring in a grown roo it can stay by its self for a little while.