They usually exercise their influence through commerce and politics. Tamil Nadu
There are a notable number of Sayyids in Tamil Nadu that mostly concentrate in the cities like Erwadi, Nagore, Madurai, and Kayalpattinam. Badusha Sulthan Syed Ibrahim Shaheed of Ervadi, a Hussaini descendant of Mohammed and a ruler of Madinah, travelled to South India in the middle of the 12th century. His descendants who live in Ervadi with the clan name Levvai are from a single forefather and are Sayyids. The heirs of Shahul Hamid Abdul Qadir badusha of Nagore who live there and are called with clan name of Sahib or Saab or Saabu are Sayyids. Kazi Syed Tajuddin the son of Mufti Jamaluddin al Maabari who founded the Kazimar Big Mosque in the 13th century the first mosque in Madurai is a Hussaini descendant of Mohammed and hence belong to Syed family. Until recently, his descendants (Syeds-Qazis-Huqdars) lived in the same Kazimar Street locality in the center of Madurai city for over seven centuries and managed the Kazimar Big Mosque constructed by their forefather. Syed Tajuddins younger son Kazi Alauddin lived in Kayalpattinam and his shrine is found there.
In her book Pain and Grace: A Study of Two Mystical Writers of Eighteenth-Century Muslim India, Dr. Annemarie Schimmel writes:

Khwaja Mir Dards family, like many nobles, from Bukhara; led their pedigree back to Bahauddin Naqshband, after whom the Naqshbandi order is named, and who was a descendant, in the 11th generation of the 11th Shia imam al-Hasan al-Askari. Although Shiite historians generally reject the claim that Hasan al-Askari fathered children other than Muhammad al-Mahdi, Bab Mawlid Abi Muhammad al-Hasan writes, in the Shiite hadith book Usul al-Kafi:

When the caliph got news of Hasan Askaris illness, he instructed his agents to keep a constant watch over the house of the Imam...he sent some of these midwives to examine the slave girls of the Imam to determine if they were pregnant. If a woman was found pregnant she was detained and imprisoned....

Africa
Most of the Muslim historians claimed that three of the descendants of Ali ibn Abu Talib migrated into Somalia and Ethiopia. The two Ashrafs migrated to Ethiopia and the remaining sayyid settled in Somalia. Ethiopia
Most of the Muslim historians and geologists claimed that one of the Ashrafs called Hajji Ali migrated into southern part of Ethiopia. After he migrated there, he got a baby and named him Gen-Silte. His children then called by their fathers name "Silte". according to the Silte tribesmen, the father of Hajji Aliyye(Hajji Ali) was Hajji Omar bin Osman, who was an Arab. He used to live in Hijaz, now part of Saudi Arabia.