It all depends on the quality of the class instructions or the how clear the book patterns/instructions are.
I have bought books that are confusing and some that give very good step by step instructions.
If the instructor is good, the class is better plus they usually have handouts and you can take notes. And if you do something wrong, they are there to show you the correct way.
And, sometimes they offer a store discount if it's taught at a store or they might have a stack of their books for a discount.