For the Vedic Hindu followers they need to know their Gotra and Pravar as it has to be spoken out in various religious ceremonies like, wedding & post death ceremonies like Shradhha, Paksha, and Uttarkriya.
(Bhavishya Purana, Part-9)
The Saint says: O Brahmin! it is important to know Gothra ( clan, or lineage – exogamous and patrilineal – whose members trace their descent to a common ancestor, usually a sage of ancient times ) or Pravar (this is said to be the father of Gothra rishis), so it is important to know the Gothras through father, teacher and by science.
Any work done without knowing proper Gothra-Pravar rishis can give bad results.
Kashyap, Vashishtha, Vishwamitra, Agniras, Chawan, Moukunya, Vatsa, Katyayana, Agastya etc are the Rishis (sages) who created gothras (lineage).
In gothra there are 1, 2, 3, 5 and so on Pravars.
One cannot marry within the same gothra, being individuals belonging to the same family; hence it is advisable to have the knowledge of lineage.
In fact, the whole universe has been created from Kashyap Rishi. So those who do not know their Gothra/Pravar they should know it from their father and if they do not know then they could consider them to belong to Kashyup Rishi Gothra and perform all the rituals as per vedic scriptures.