Some quotes from a interview with Milt Kahl in the book Walt's People.

Dr Moritz: Did you do those model sheets where they have six poses of the character?

Milt: They'd take a lot of drawings from my animation and make a model sheet of thosee.. It was much better that way because the model department.. they couldn't really draw that well anyway.. When something gets into animation, it forces itself into a different design. Especially heads. Faces. Because to articulate them, there were certain things that just didn't work.

Dr Moritz: That's true with the beginning of Snow White. They had a lot of problems articulating her.

Milt: Yes. That's just inability to draw. The judgement of how not to draw something. .

Those quotes just confirms how important having a hand drawn animation ability is so important in doing character designs~