If your Euphorbia Royleana ever experiences root rot or any other potential diseases, using fertilizer is recommended as an additional tool to bring their health status back up to "healthy." However, you can use it as you choose, even if it's just a little growth booster for your succulent. Exposing it to too much direct light could be devastating for this plant, especially if it's not acclimated to full sun or if it's a new plant from the store, or if it's a young, baby jade plant.