Although not as detailed, the separation and description of territory for the Israelites serves the same literary function (challenge?) as the description of ritual served during the exodus. It is interesting how quickly the story details cracks in the idea of absolute war in which the enemy was absolutely destroyed.
Already, there was the story of the wood workers and water carriers who were evidently not Israelite. Then, in the cities of Mennaseh and Ephraim there are still Canaanites. Sure, they're enslaved by the power Israelites, but they are still there. When they complain to Joshua about not enough territory, his response is for them to man up and take the territory in the forest still held by the enemy. Recall, that is exactly what Caleb did.
We are seeing the divisions that will be featured in the book of Judges.