There are plenty of ordinary situations when you cannot rely on just a single star, thus a compass was invented. The Southern Cross is more like a Southern Big Dipper. Just easy to identify (even though I had a trouble doing that at the first time long ago, as somehow expected a star in its center ), but it is quite far from the true South point for any compass calibration. My point is that a planetarium app on the phone can help you with any celestial navigation tasks from just objects identification to a serious sextant work.