Any good epic fantasy novel starts with a map!
I cannot think of any exception, even if the authors eventually decide not to show their sketches and scribbles, all of them started from here; The base.
Surely there are books without maps and worked even better this way, but conceptually human minds need the support of a visual asset to progress a tale.
Your heroes; wizards, witches, elves, dragons, orcs, trolls, ogres and other mighty creatures, need to be placed somewhere. And, if like me you are more of a visual person, having an image of some sort to immediately relate to the chapter you are writing about it's very helpful and makes the story flow more naturally.
And not only this, your story improves at the same pace of your imaginary world - they go hand in hand. If you have a great plot, great characters but your world is rather poorly conceptualized then everything suffers.
The grass is green, the sky is blue you can find in any given story, but the green grass of your precise world with that blue sky of your specific place, exists only in one tale: yours.
There are many ways to go about creating it and no other style can be better than what you will chose, because it will represent your own choices and purpose.
From the epic Lord of the rings famous map, masterfully detailed and crafted, to the simplest of all, basically an outline in Markus Heitz's - Dwarves series, you can do whatever you like and be just as efficient as the other authors have been.
In my case, I have based my world around an island, the deep ocean surrounding and fighting against the land in a timeless conflict has something more appealing and way more powerful than a desolate endless land (unless of course it has to be this way for the main plot to be working).
The Aranthian Empire - Tokens of Benevolence
Whilst many decide not to show and use one for various reasons, I think I can understand where the main frustration of having a map can derive from; it takes a long time to build a decent map and an author cannot be bothered with it - an author wants to write, period.
Yet, in my opinion, it is an investment worth your $.
The benefits of having a map for your novel and use it inside your book!
1 - The best tool for your, the author, to use in the early stages of development and writing your first lines. It helps you understand and implement better the world and its characters to your liking.
2 - I would say it is incredibly helpful both for you as an author and secondly, and most importantly, for your readers. Everything makes sense inside you author head since you've concocted the book out of thin air, so make it as easy as possible for the readers as well.
3 - It is stylish and cool to have a well drawn map that welcomes and introduces you to the novel at hand (in whatever style pleases you and your readers).
4 - Easy to navigate when bouncing back and forth between chapter's locations.
5 - A great graphical asset to have if you suddenly become famous and would like to sell some merchandise art for your devoted readers ( everything that ranges from purses, T-shirts, wallets, wallpapers and mugs)
So, personally. when asked; "Does every fantasy novel need to have a map in it?" I would be tempted to reply Yes!