Does knowing if "Young Goodman Brown" was a dream make a difference in your interpretation of the story?

In terms of allegory, the ambiguity of the dream is what is really important, so yes I guess it is vital to your interpretation of the story. Hawthorne obviously left the dream up in the air for a reason.

When I teach "Young Goodman Brown," though, it really doesn't make much difference to me whether it was a dream or not. The importance is the change that occurs in Brown. He is never able to really know for sure if the black mass in the woods was real or not. But it does cast a shadow over his life and cause him to die as miserable old man.

As long as my students can understand that it was Hawthorne's intention to leave the reader wondering if it all really happened or not, I am pleased. Of course, they take sides and argue them.

So if you're thinking Brown dreamed everything, what does that say about his guilt and his subconscious desires and fears? If it was real, what does that say about his fellow residents and his own history?

The important thing to learn the story is how Young Goodman Brown changes throughout the story. He leaves a naive, pure young man. However, in the woods he has his eyes opened to the hypocrisy around him. He even learns (or at least the reader does) about the true nature of his supposedly pious family (there is a reason the devil is so familiar to him). Instead of recognizing that humans have a capacity for evil and then doing something about it. Brown refuses to accept it and dies miserable.