I'm not sure what you're referring to? I usually make that sort of decision on a file-by-file basis (if there's just one or two references to ```std::string```, I don't do a ```using```).

You may have noticed that I did remove one ```using std::string;```, but that was in a header, and the style guide specifically forbids that (and for good reason!), so that wasn't as much of a personal call.