Just like in any religion, there are many more subdivisions and sects than just the larger overall factions. Within Sunni and Shia, there are extremely diverse ranges of beliefs. Salafism is a sect of Sunnism that believes that only the laws and practices of the era that Mohammad lived in were valid. Deobandism on the other hand is extremely heavy in academic analysis and refinement of Islamic jurisprudence, and is very famous for its scholars wanting to debate other religious scholars on theological grounds. They have a very large body of works that they consider important treatise on Islamic law, and Salafists often accuse them of not being true Muslims because of this. Sort of a Lutheranism (Deobandi) vs Fundamentalism (Salafi) dynamic.