Poipu is spread along curving resort roads, so walking works best for beach-to-beach wandering, not for every errand. The stretch between Poipu Beach Park, Kiahuna, and the main shopping areas is manageable on foot if you are patient with heat and traffic.
Use a car for Spouting Horn, the botanical garden visitor centre, Koloa, and any island-wide exploring. Parking fills early at the most popular beach lots.