Qt for Python (PySide/Shiboken)

I'm developing an application that requires heavy background tasks, using QThread. But also, after reading, Slot options are offered for transferring information to streams. I also tried using just a global instance of my settings class, and I successfully change attribute in classes at any stage as well as reading them. What's the point of using Slot then? or is it just to maintain the code structure of c/c++ languages? (I know that global variables are bad, but I think it's very good to make global settings so that don't always transfer between threads all the time)