I feel like locs are a protective style in themselves. Of course, the same rule may apply for shoulder length locs that applys for shoulder length hair-the ends will rub against the fabric of your shirt and lead to breakage. So I'd say when they get to that point keep them off your shoulders in a pony tail/pig tails.
I know people do different cornrowed styles for the sake of trying something different, but not necessarily as a PS.
