Birds Choice Premium Aluminum Purple Martin House – 12 Room, 3 Floor Birdhouse with Starling Resistant Entrance Holes, Ventilated Roof & Easy Cleaning, Unassembled

I'm assuming it's just for visual interest. Each orb can have one nest in it, each of the box style nests looks like it is big enough for 12 nests per box. 6 per floor facing back and front, with two floors, kinda like these https://www.amazon.com/Birds-Choice-3-Floor-12-Starling-Resistent/dp/B001QF0IM8