I was sitting in class at City College once, not taking notes – drawing instead. One of my peers looked over and asked what I was doing. I turned my book so she could see a sketch of one of my favorite main characters.
It wasn’t enough for her. “Who’s that?”
I told her and she asked, “You draw your characters? Why?”
Now it was my turn to be confused. “Why wouldn’t I?”
Writers are taught that in prose, it’s a clever tactic to leave the physical appearance of characters to readers. Give them guidelines – simple descriptors that create an image of the kind of person someone is. You could say, for example, that Rock Stout had golden hair, perfectly curled, and wide teeth that almost glistened when he smiled they were so white, and from that we’d generally get that Rock Stout was an ass – or probably an ass.
The same occurs in Fantasy writing. The simplest description in the world is “he had a chest like a barrel.” I’d almost be worried about quoting someone specifically, but this has been said in so many ways in so many stories that I believe it’s impossible to quote anyone specifically with this, and – furthermore – I’m not saying this descriptor is a bad one. The point is, we get everything we need to know from that phrase: this man drinks, laughs loudly, probably uses an axe or warhammer, probably likes wine and whores, is possibly a black smith. It’s simple – about as simple as Rock Stout’s description. Likewise, our hero can be simply described as “usually the tallest head in a room” and again, we get the idea.
The question then is, why bother doing more than this? Why devote as much time to character design and artistry for a media that barely needs it?
The answer is simple. Because I don’t want this to happen:

This is the US cover of Robert Jordan and Brandon Sanderson’s The Gathering Storm. And, sadly, it’s probably the best cover for the series so far, or among the best.
Now, let’s see what happens when, Seamas Gallagher, who takes his time and, more importantly, cares, renders Rand Al’Thor:

So, what am I saying here? Is it that all fantasy writers should spend time trying to draw and design their characters? That even if they do, the artists assigned to do their cover art somehow will – or will even try to get it right? No. What I’m saying is that when War of Exiles is released, if it has a cover that looks as off base as this –

– you can come back here and look at the awesome character sketches and art that I’ll have up by then until the pain stops and the tears go away. Mine and yours.