Yeah, what does that option really, actually and effectively do? It sure doesn't export the piece in real time, or then I just don't know what "real time" means. Does it provide for better/worse quality or does it do some other mystic stuff?
there are some nasty plugins that seem to have inner workings not suitable for the normal rendering to wav. in these rare cases rendering in real time could help, where mt will play back the song and instead of sending the output to your soundcard it'll record it. however, sometimes even this won't help with certain vsts...