For me: the chicken door goes into a fenced enclosure to keep the chickens safe from predators.

I don't want to enter the enclosure, so I have my own door to go in and service the coop, fetch the eggs, etc.

The enclosure has a gate when I want to let the chickens out, as well.

Having an enclosure lets me leave the house for a couple days, at least, and not feel like I've imprisoned them.