Board Thread:Theories and Speculation/@comment-25139119-20150508231130/@comment-5936871-20150508231429

The tailed beast can only communicate with each other telepathically within a limited range. They cannot commune with each other if they are all dispersed over the world. Therefore, by leaving some of their chakra and consciousness within Naruto, whenever they wanna talk to each other, they can enter that part of Naruto's subconscious and talk to each other no matter where they are. Which allows them to keep in touch with each other and remain unified.