1) Greek philosophical traditions thrived in the Shia world, unlike in the Sunni tradition, and developed into mysticism, which became very popular in Shia teachings and was taught and used by many Shia leaders.

Sufism, on the other hand, did not find as much popularity with Shi’ism as it did with Sunnism, due to seeming inconsistencies with Shia beliefs, but Shia Sufism did manage to survive despite some attempts at suppression throughout the centuries.

2) I found it interesting that Sufism does not actually follow the Sharia, but they follow a more spiritual path that they call “Tariqa”. Shiism actually includes “Tariqa” as well as the Sharia, so despite the unpopularity of Sufism in most Shia communities, Sufi orders still seem very much incorporated into the Shia tradition.

(Source: “Shi'Ism and Sufism: Their Relationship in Essence and in History” from Jstor.org)