The audio commentary to the 60th Anniversary Edition of Fantasia has many comments by Walt Disney, often in his own voice (rather than someone reading something he said). Of the leaves in the final segment of The Nutcracker Suite, Disney said this (emphasis mine):
Have perfect control of the leaf. Make the leaf do all the movements we want it to do. I don’t like it where it gets down and dances; we’re limiting the leaf to what a human being can do. That’s another thing. We could make a comedy out of this, but I don’t think we should. Take a floating leaf and the shapes it might assume. Like when the leaf floats down and lands on the ground and the movement of the wind. You’ve seen them in a high wind. Try to take the natural movement of the leaves and things like that being tossed around in the wind. A ballet effect.”
I've noted before on New Savanna that animation seems an inherently object-oriented medium. Everything had to be drawn by hand, sticks, stones, apples, cats, and people alike. And anything and everything could be and often was brought to life.