This is a very personal decision. People who swear by poles tend to be older, or they have knee or foot issues. But even if you have youthful knees, a set of poles can help you with stability and managing your weight load. If you already hike with poles, bring them. If you don't normally use them, try using using poles on your Camino training walks and see how they feel to you. And if you don't take them but later want them, you can always purchase inexpensive poles in the larger Spanish towns.