what's exactly meaning of "Enables overriding of any property reference with global properties"?

Yes, I tried  -G option in my command-line with both override option checked and unchecked.  in both case, my test picked up passed in value rather than the value saved in my soapui-settings, made me become more curious about what's the purpose of the option, what's the potential impact if I check or un-check it. 

Thanks,

Sizhou.