The good or evil effects of planetary transit through stars get neutralized by occupation of certain specified stars by planets reckoned from the stars occupied by the planet under consideration. This is called Nakshatra Vedha. These are in all 16 (two each for the 7 planets and 2 jointly for the nodes) position as under:
In order to understand the above, suppose the Sun is in Ashwini Nakshatra in the birth horoscope. The 9th Nakshatra therefrom is Ashlesha. When Rahu or Ketu moves in Ashlesha Nakshatra most of the good effects indicated by other planetary transit will be suspended and only malefic effects will come to pass.
Again, the 15th Nakshatra from Aswini is Swathi. When Ketu comes to move in Swati, similar effects are expected. In the same way, the other Nakshatra Vedhas as above should not be ignored in considering any transit effect. It is a different matter, if the directional influences are particularly favorable to the native.