what are the propose on vinyl-buffer and gulp-streamify in gulp?

as the documentation says, they both deals with transforming non stream plugins to stream. but what I try to understand is if if I can I use the .pipe() method on something, isn't it mean that it's a stream? if so, what I convert what here?

vinyl-source-stream example:

(from: http://ift.tt/1EoInyw)

var browserify = require('browserify')
var source = require('vinyl-source-stream')
var buffer = require('vinyl-buffer')
var uglify = require('gulp-uglify')
var size = require('gulp-size')
var gulp = require('gulp')

gulp.task('build', function() {
  var bundler = browserify('./index.js')

  return bundler.pipe()
    .pipe(source('index.js'))
    .pipe(buffer()) // <---------------------- why doing it?
    .pipe(uglify())
    .pipe(size())
    .pipe(gulp.dest('dist/'))
})

gulp-streamify example:

(from: http://ift.tt/1EoInyy)

var source = require('vinyl-source-stream')
var streamify = require('gulp-streamify')
var browserify = require('browserify')
var uglify = require('gulp-uglify')
var gulp = require('gulp')

gulp.task('browserify', function() {
  var bundleStream = browserify('index.js').bundle()

  bundleStream
    .pipe(source('index.js'))
    .pipe(streamify(uglify())) // <----------- why doing it?
    .pipe(gulp.dest('./bundle.js'))
})