These new lands, with their own histories, politics, and geography, really go a long way in putting the 'fantasy' into fantasy novels. The idea is to give us a handy reference guide to this entirely new world that we'll be exploring. A lot of fantasy novels (like The Lord of the Rings and the Game of Thronesseries) start off this way.
When a book starts with a map, you know that the setting is going to be a big deal. Alagaësia, the Hadarac Desert, the Boer Mountains