With Global Send Keys you can only interact with the application that is currently attached. For example, in you use GSK with Notepad, BP will be able to send the key strokes only to Notepad.
With Global Send Keys Events, you can send keystrokes to ANY application that is currently active, regardless of if it's attached or not. With the same example, let's say that you are using GSK Events with Notepad but an instance of Excel is activated, then BP will send those keystrokes to Excel.