Yes, but it’s always best to take them off after each use to maintain their quality over time. The more your clothespins are exposed to the elements (sun, rain, etc.) the faster they will degrade.  Additionally, clothespins left on the line will inevitably get dirty. The wind, rain, dust, and dirt will collect on your clothespins over time and that dust can transfer to your clean laundry. Avoid all of this by investing in a great clothespin storage bag and taking pins on and off the line as needed.