Rahu Puja is performed for those who has malefic effects of Rahu in their horoscope.
Rahu (Dragon's Head) is one of the Graha from Navgraha in Hindu Mythology. Rahu is a shadow body. Rahu in Vedic astrology rules the natives fortune, spiritual, atheistic belief, abstract nature, honesty, truthfulness, old age related disease, past life karma and alcoholic behaviour. It also represents possessiveness, misbehaviour, panic displeasure, passion, fascination and uncertainty. It is also an enemy against the Sun and Moon. Due to it there are eclipses. It is believed to be the king of meteors. Rahu represents the ascension of the moon in its precession rotation/ around earth. It is considered as a Malefic Graha in astrology. Usually Rahu and Ketu are paired.
In the presence of Rahu a person can have unlimited Wealth but will never help anyone. A frequent lier who always think about his/her benefits. Due to its malefic effects a person can be caught in legal issues and will also loose money in business or share market. The person will have lack of judgement and bad in planning. In the bad influence of Rahu a person have bad relationship with relatives , can have only few friends.
Rahu also causes bacterial diseases. It is favourable if placed in 1st, 3rd, 6th, or 11th houses in someone's horoscope. It is also beneficial if placed in Aries, Taurus, Gemini, Leo, Virgo, Sagittarius Zodiac signs. Rahu presence in someone life would be about 1.5 years. Usually it take 18 years to complete a Zodiac Cycle.
At the old age person may become spiritual and live rest of his/ her life alone.