I do not pretend to understand this but to those that do, have at it:
When building a UI with Unity3D’s UGUI system, it’s usually important to make your interface scalable and easy to extend. There are also many cases where the number of items in your UI is dynamic. The components I’ll cover here are all designed to make layout easier.
It's impossible to remember everything. Having a "reference" to "refer" back to is important when you are just starting out on Unity3D. Here are more reasons why: https://www.youtube.com/watch?v=QnOo9NjT_w0