I feel that quarantine is a personal choice - neither right nor wrong. The thing is, so many people don't have the room to do it properly and think that sticking a new chicken in a cage or pen next to the flock is "quarantine". When it's advised on here to "quarantine your birds" that advice...
I integrated my 30 chicks with my 6 adult hens when they were about 6 weeks old. They had all shared the same coop (separated by chicken wire) since I got the chicks as day-olds. They were in a brooder box for about 2 weeks, then given the run of their section of the coop where the hens could...