Matching horoscopes of bride and groom before marriage is a common ritual in India. This is done to see if the couple is astrological compatible and will have a healthy future together.
According to the Vedic astrology, Nadi is one of the important 8 kootas that is matched before a couple's marriage to find out if the marriage will be a good match or not.
If the birth star of bride and groom who are going to be married comes into the same Nadi, it becomes a bad combination and this is known as Nadi dosh. For a perfect married couple, the Nadi of the proposed groom and bride should be different.
Same Nadi is also considered to be near akin to same blood stream which in some cases not a good sign for reproduction. One should not take Nadi Dosha for granted and before getting married, they should pay attention to this problem. However, there are some Naxatra and Rashi where Nadi Dosh is not applicable.