By the end of the story, we've never seen a stranger looking group of people in our lives. There's Mr. Wonka, with his crazy outfit, looking down at all the other children, stretched, blue, and covered in trash.
Why does Dahl bother with such physical descriptions? Of course the more he describes, the more we are invited into the book, and the easier we can imagine the world for ourselves. But appearances are also part of a greater lesson. Think of Charlie early on in the book. He's skinny, coatless, and clearly very poor. Passing him on the street, you wouldn't guess he would one day go on to own a chocolate factory. But that's just it – appearances can be deceiving. So while appearances in Charlie and the Chocolate Factory may seem like just a quirky way for Dahl to have fun, he's also showing us that things don't always appear as they seem.
Appearances can be a useful tool; they help the characters in the book size up the people around them.
Willy Wonka is so odd-looking, not because he's odd, but because he hasn't been outside in years. If he had, he wouldn't be so weird.