To understand turns on runway you must understand the whole nature of runway. What for models are making turns on runway. But runway modeling is not a ballet. Fashion show is not just a show. Main goal of any fashion show to promote, advertise and sell.
Fashion show can promote, but bad fashion show can destroy even a good collection.
Please remember the answer. The model make different turns on runway because they help to show all outfits in the best possible way. Only collections, only outfits dictate the style of show, kind and quantity of turns. Some outfits don't require any turns and some require several turns. Very often you can see that model make the same turns and in absolutely different collections, absolutely deferent styles.