Directors dont always have input into character designs for a TV series, but they should. There are many design issues that have enormous impact on production. Design is far more than how a character looks.
In drawn animation, the amount of pencil mileage the number of lines on a character has a direct effect on how long it takes to do a drawing. The number of colors on a character determines how quickly color can be applied, whether its by hand or by a digital system. Both of these things have an enormous impact on the schedule. If each image of a character is going to take a long time to produce, youre going to get less animation.
In computer animation, a big issue is intersections. While 3D characters look solid, there’s nothing to stop one surface from penetrating another. A character can easily push his hand through a table or his own body. When youre dealing with capes, skirts or long hair, you have to be concerned about the potential for intersections. Even something as simple as the design of a character’s neck might lead to intersections when the character talks or moves his head.