Why is there so many return statements in node.js

I am reading a book on backbone.js, and there's an exemple using node.js to build the backend of an API. Link to the book: http://addyosmani.github.io/backbone-fundamentals/

At some point there is this code

//Update a book
app.put( '/api/books/:id', function( request, response ) {
    console.log( 'Updating book ' + request.body.title );
    return BookModel.findById( request.params.id, function( err, book ) {
        book.title = request.body.title;
        book.author = request.body.author;
        book.releaseDate = request.body.releaseDate;

        return book.save( function( err ) {
            if( !err ) {
                console.log( 'book updated' );
                return response.send( book );
            } else {
                console.log( err );
            }
        });
    });
});

I don't understand why there are so many return statements, as this code works as well without the returns

//Update a book
app.put( '/api/books/:id', function( request, response ) {
    console.log( 'Updating book ' + request.body.title );
    BookModel.findById( request.params.id, function( err, book ) {
        book.title = request.body.title;
        book.author = request.body.author;
        book.releaseDate = request.body.releaseDate;

        book.save( function( err ) {
            if( !err ) {
                console.log( 'book updated' );
                response.send( book );
            } else {
                console.log( err );
            }
        });
    });
});

Did I miss something?