In the Indian Astrology, Kalsarpyog is very important yog. The major reason of kalsarpyog is Rahu & Ketu (both are Chhayagrah).
How Kalsarpyog happen:
When in a Kuldli all planets (grah) came in the one side or between Rahu and Ketu, then kalsarpyog happens.
There are 12 types of kalsarpyog in Indian Astrology, As Rahu moves in Meen, Kumbha, Makar, Dhanu, Varishka, Tula, Kanya, Simha, Kark, Mithun, Vrish, Mesha rashies then different types of kalsarpyog become.
Only some yogs are beneficial, it become famous person but need struggle in life, it depends on the birth kundli of person rest are harmful and the person must do struggle for his / her life.
Example: Lata Mangeshkar has a kalsarpyog in her kundli.
With best regards