Curly hair when wet tends to straighten out, so when you're cutting it can be hard to judge how long it will be while it is straight, so as it dries it goes back to its original shape being curly and when it curls it is "shorter" than when it is long. That's why you have to wait while cutting.
As an Artist I think it depends on which piece of art it is and how you feel. Personally I like charcoal. On art medium they don't really talk about is oil paintings. They don't like teaching it because it a more complex medium.They mainly focus on acrylic paintings.
