[obsoquasi]

E(TTL) is only possible over either a E(TTL) cable or a PocketWizard that supports E(TTL). PC Sync cords are just for triggering a flash whose power you have to set manually. In controlled situations where the light doesn't change that's no big deal, as long as you have easy access to your external flash - in this case you use your camera in manual mode anyway, so everything is locked down perfectly and you can concentrate on shooting. But if the light changes, your subject moves a lot, E(TTL) helps you determine your flash power from exposure to exposure, which can make your live easier. But I have to say sometimes more unpredictable as well, because you are not in full control anymore. For macro you don't need E(TTL), for posed portraits neither, for journalistic kinds of portraits you might need it though - because the external light conditions change very often between your shots.