Am I abusing static classes if all I want is a quick reference?

After getting used to using Singletons when it is important to only have one instance of a class at a time, I kinda developed the habit of using static classes for quick reference while forgoing the whole Singleton thing.

Code (CSharp):

1.     private static LevelManager instance;
2.     public static LevelManager Instance
3.     {
4.         get
5.         {
6.             return instance;
7.         }
8.     }
9.  
10.     private void Awake()
11.     {
12.         if (instance == null)
13.             instance = this;
14.     }

Sometimes I have classes that just use LevelManager in one or two lines of code, so instead making a variable and using something like FindObjectOfType<LevelManager>(), I just use LevelManager.Instance.

Is this bad practice? Particularly when it comes to performance? I can understand that I should limit the amount of classes that are allowed to access and modify my LevelManager, in this case every class, but my project is small and I think I can handle it. I don't like using serialized Fields either because that's where errors happen: Sometimes I have to reassign everything manually after changing the scene.

Thanks

 

Is this on a monobehavior attached to a GameObject? I'm not experienced enough about Unity to judge the pattern as a whole, but if it is used I would consider it bad practice not to check if there already is an instance and warn if a second one is created (assuming there can only be one). Defensive coding helps your future self.