Why does compiling .sass to .css (with gulp-sass) create an extra folder?

Question

css

When I compile .sass, .css is created in the specified path, but additionally in the sass folder, it's not clear why.
Specified:
.pipe(gulp.dest('app/css'))
A is created as if the code looks like this:
.pipe(gulp.dest('app/css/sass'))
Here is the full gulp-sass task:

gulp.task('sass', function(){ // Создаем таск 'sass'
  return gulp.src(['app/**/*.sass', 'app/**/*.scss']) // Берем источник
    .pipe(sass({outputStyle: 'expanded'}).on('error', sass.logError)) // Преобразуем Sass в CSS
    .pipe(gulp.dest('app/css')) // Выгружаем результат в папку css
    .pipe(browserSync.reload({stream: true})) // Подгрузка стилей в браузер
});

Answer 1

The reason in
The output takes into account directories ** , like this will not be:

gulp.src(['app/sass/*.sass', 'app/sass/*.scss'])

// или
gulp.src( 'app/sass/*.{sass,scss}' )