The Book Trailer is the appetizer to your Book Feast
An interesting thing happened when I was talking with a few author friends. They said, "Do I really need book trailers to market my book? Why can't I just worry about writing my book and throw it on Amazon and leave it at that.?"
Now I told him you can do that but you won't be completely satisfied and you will leave some things on the table. If you aren't showing your book in the best possible light to increase awareness, interest, and hunger to read your story then you are leaving readers at the table.
Consider a book trailer an appetizer. You go out to dinner, but what does the waiter who comes to your table always ask you before the main meal (your book)? They ask, any appetizers?
Now like book trailers, some who dine say yes I will take the boneless wings, and some say no thank you. The only thing you are missing by not ordering the appetizer is you are not enjoying the full experience and feeding your stomach entirely.