The difference between Jaggery and sugar is their composition. Sugar is that the simple sort of sucrose which gets digested faster and energy is released immediately whereas Jaggery is formed from longer chains of mineral salts, sucrose, and fiber.
Since, Jaggery is ready in iron vessels, it's rich in iron. Jaggery consumption is suggested over sugar in cases of patients with iron deficiency. It also acts as a cleanser because it helps clean the lungs and tract . So, it's advisable to substitute sugar with Jaggery.