Using shared variables instead of global variables

[GuyM142]

This year we have a big amount of global variables and it becomes hard to find the one I need each time.
Separating the variables to different global variables also isn't ideal because I have to drag the correct one and only then choose the one I'm looking for.

I've noticed that shared variables can be chosen very easily by library and I wish to use them instead.

What are the differences between those two types?
Is one of them more efficient than the other?

Thanks!