Ketu is the planet of extremes, though Rahu is also. But Ketu can be much much more benefic or even malefic than Rahu. Ketu is much more intense than any other planet. Ketu is a mild malefic planet, less malefic than Rahu, but it can act in both ways, beneficially or maleficially.
Ketu is a psychic planet, he gives things in big amounts and suddenly. You should understand that Ketu is like crystal clear water, which changes its colour very quickly, depending on other planetary influences.
Ketu is the co-ruler of the scorpio sign.
Though Ketu is a spiritual planet, and represents all kinds of supernatural power. If horoscope is spiritual, then Ketu will give all ability to attain salvation, that kundalini power is in Ketu. A benefic Ketu shows “daiva bala”. Now, how this god’s grace is utilised, will depend on complete horoscope.
Like: if horoscope is materialistic then a lot of good inheritance, less struggle in life etc etc. If spiritual then, supernatural power, siddhi etc.
Rahu-Ketu has no aspect. They are shadow planets and can’t aspect. No major classic has clearly written about their aspect.
Logically, it is correct too. Think, Jupiter is only a single natural benefic planet having special aspects, then two natural malefic planets have, Saturn and Mars. If we give another malefics Rahu-Ketu aspect, then what will be left in the horoscope, horoscope will be ruined. Can a single Jupiter work? No.
They don’t even have a 7th aspect, because Ketu or Rahu will always be opposite to each other, so their influence is always on an axis.
Ketu has similarities with Jupiter, Mars and Sun. This makes Ketu spiritual, but he can be a criminal as well. Logically, he has no head. So, he cannot think, whatever comes to it, he accepts. But he helps in research he goes into deep meaning. For example: Mer-Ketu conjunction, if this conjunction is good and mercury is strong then Ketu will give a tremendous amount of intelligence. But, if afflicted, the native can be confused and make bad decisions in life. There is always an unusual thinking and intuition with Ketu, and this can be good and bad both.
In the chart of spiritual persons, if Ketu is afflicted they fail to attain the beauty of spiritualism. So, with Rahu in the chart of materialistic people.
Rahu-Ketu gives results according to their sign lord, and planet associated. They always promote the results of any yoga. If bad, then worst and if good, then excellent.
They are not always retrograde, if one is taking true nodes(calculation). And true nodes should be taken also. They become direct when the Moon is close to conjunct them, at the time of eclipses also. And their motion matters a lot in deciding their results.