In my opinion there are 3 main ways to use Globals:
WAY 1: The same Global on multiple pages
When you create a Global all the components of that Global become by default integral parts of the Global, so if you place the Global on multiple pages and then modify its content on one page, those same changes will also be propagated to the instances of the Global present in the other pages.
It is an excellent solution when you want to have the same page section present in multiple pages, because if you need to make a change this will then propagate to all the other pages, without having to manually modify each section.
WAY 2: The same Global on multiple pages but with different content/properties of the components inside it
If you have a Global, which you want to remain structured identically in all the instances you place on the pages (and by “structured” I mean with the same components inside it positioned in the same way) and you only want to change the content/properties of some components inside it, then, for each property you want to change, you must first click the small Unlink icon (see first screenshot). That icon is only present in the components inside a Global and is used to make that instance independent from the Global. So, for example, if you want to change the size of a Text component in a single instance of the Global, you will have to select the Text component and click the Unlink icon of the Size property.
In the same way you can change any other property of the component.
However, all the properties that are changed exclusively in-page are an exception (such as the text content of a Text component, you change the text directly on the page and not from the Inspector panel). For these properties you must open the first section of the Inspector panel Global Overrides and highlight the property you want to modify (see second screenshot).
WAY 3: The same Global on multiple pages with a different structure
If you want to have a different structure, that is, have different components within the same Global positioned on multiple pages, then you must unlink the contents of the Container (Global Overrides section of the Inspector panel). Once the Container is disconnected from the Global, everything you modify inside it (including the addition of new components) will no longer be propagated to the instances of that Global present in the various pages.
CONCLUSIONS:
However, no one is stopping you from merging the three modes into a single Global, and therefore in the same Global you can have identical components on each page, components with only the properties modified and components structured differently.
Also remember that you can go even further, inserting a Global inside another Global.
FEEDBACK FOR @dan
You could consider coloring in a different way from green (for example magenta) those components of a Global to which at least one property has been disconnected. In this way, when we move the mouse hover the Global, it is immediately clear which components have been modified within a Global.
