If I only instantiate a class once should I make all its vars static?

If I only instantiate a class once should I make its vars static?

I understand how this is of benefit if I make multiple classes, clearly you use less memory as it creates a reference to the same place for each class. Are there any other benefits for creating static vars or functions ?

For example I have my class ‘MainMenu’ which I create once (might even be my document class). In it I create a

private var someHolderForStuff:Sprite = new Sprite();

should I rather create

private static var someHolderForStuff:Sprite = new Sprite();