The function is to give an example of obedience to the people of Joseph. Just like Caleb back in Joshua 14:1–15, seeing these five daughters go to claim their inheritance was meant to provide inspiration and encouragement to God’s people. God kept his promise to Zelophehad's daughters. He will keep his promise also to you, therefore be brave and go and live in the land.
3 Now Zelophehad the son of Hepher, son of Gilead, son of Machir, son of Manasseh, had no sons, but only daughters, and these are the names of his daughters: Mahlah, Noah, Hoglah, Milcah, and Tirzah.