Town lifestyle (I assume you mean by this: a settled lifestyle , so that it contrasts with the nomadic lifestyle) comes with more security: you can store your food reserves and plan for the future.
nomadic lifestyle gives you more flexibility but less security: you can travel elsewhere if your fodosource is runnign low... but usually this is not as good of a food source as a settled lifestyle. One other possible advantage could be being merchants: nomads can benefit from a trade.