Load menu via SceneManager

I'd like to know if it's a good or bad idea to load the main menu, options and other GUI-stuff via the SceneManager's async-method (additive) into my game (Unity3D).

The idea behind is that the game might not need so much memory if I load all of the GUI (main menu, options, level selection, achievements, etc.) asynchronously (additive) in my game. Please - can someone help me, please?

This is some code I found but it doesn't work:

Code (CSharp):

1. IEnumerator loadNextScene(){
2.     string name = "ALegitSceneName";
3.     AsyncOperation _async = new AsyncOperation();
4.     _async = SceneManager.LoadSceneAsync(name, LoadSceneMode.Additive);
5.     _async.allowSceneActivation = false;
6.  
7.     while(!transitionIsDone){
8.         yield return null;
9.     }
10.  
11.     _async.allowSceneActivation = true;
12.  
13.     while (!_async.isDone) {
14.         yield return null;
15.     }
16.  
17.     Scene nextScene = SceneManager.GetSceneByName( name );
18.     if (nextScene.IsValid ()) {
19.         SceneManager.SetActiveScene (nextScene);
20.         SceneManager.UnloadScene (SceneManager.GetActiveScene ().name);
21.     }
22. }