Not a must have by any means, but I like that I can stand at my kitchen door and look out and see my entire coop and run. While my flock is ranging the people door stands open so from my kitchen I can see their nest buckets. I can watch from an acre away and by their color and markings I can see who layed when.
My must haves... Hmmmm. I made my vertical space useful to everyone, not just me and my back. I have two main roosts where they all sleep, but there is also walkway roosts and a table/platform built around my buckets where I keep a flock block (and their feeder when its raining). Making use of vertical space means even when everyone is inside there isn't overcrowding on the floor. Everyone has a place they hang out during the day (if they feel like staying in) and a different spot they slep at night.