Character model sheets are my least favorite part of concept designing, but they are really important. Obviously, the modelers use them to build a model of your concept, but I find that it also reveals more fully to me what the 3 dimensional shapes are that make up my design.
As I have constantly found from working with 3D artists, there's always room for interpretation of a 2D design and when you work in 2D, there are a lot of short cuts that an artist takes that only work as an abstraction of reality. The way the eyes wrap around the head is often a place that where my front and side view drawings don't match up once modeled in 3D. I usually give the eyeballs much more mass from the side than would actually appear if my front view is matched. You can see the disjoint in Inspector Clousseau examples below. Check out the eyeball in the 2D profile shot. There's a solution in the 3D toy on the right, but you can see that the nose had to to be moved in order to make room for both eyes to sit together. That shift pulls the nose over the mouth as a result.
A lot of anatomical impossibilities will come up in 3D that must be worked out and agreed upon with the modelers, but working out the basic shapes of a character with abstracted anatomy really saves a modeler some time and ensures that the character looks like what I had in mind, from all sides. I've often been told by my 3D buddies that a three quarter view describes the most of any view, but it isn't nearly as helpful from a modeling stand point. Proportions in a 3/4 perspective can't be judged as accurately.
Since I'd drawn Pepe from the front and not in three quarters, I found that a lot of people had mistaken the scarf around his neck to be a collar, even with the scarf tails hanging down his back.