Script is a type of instance that should only be done once. It's very unlikely to run into problems since we're not dealing with anything that will cause that but think of it this way. When you make a class for methods that needs Script, you're not going to inherit a brand new instance of what your main class has, you want something to 'show' that it's not the main class, hence using the main class' Script instance or using your main class itself.
It's 7am and I haven't slept so I may not be explaining it properly, if someone can pitch in that would help.