Not all astrologers have made a distinction between essential and accidental dignities and debilities.
Dorotheus, Ptolemy, Valens, Paulus and other Hellenistic astrologers often group them together, for example Dorotheus and Valens compare ''inoperative'' planets in fall to ''inoperative'' planets in cadent houses, meaning that they thought they meant power, Ptolemy and Paulus likewise grouped ''inoperative'' phases (like evening retrograde) with them.
Ptolemy seems to make a distinction between the universe and the nativity only with regard to time here.
It is true that when such a distinction is sometimes made, the essential dignity is taken with regard to quality, while the accidental dignity is taken with regard to quantity, but this in my opinion wrong theoretically and experientially.
Indian astrologers have even made two distinct concepts of Ishta (power to do good) and Kashtha (power to do harm) to do deal with some related problems.
Naturally, why does Saturn become stronger to help or harm at the Midheaven? You would answer that it has more power to cool there. Then I would ask why would Saturn become stronger to help, but not stronger to harm in Libra or Aquarius since these signs increase cold in the exact same way???
But you ask doesn't Saturn sometimes give great wealth and power to nativities, and doesn't he sometimes cause great afflictions? Yes, of course, but that has to do with his harmonious or disharmonious relationship with the planet/angle/lot through the different aspects and natures of the subjects. So combining essential and accidental dignity into the same concept does not prevent us from making these distinctions, while I would argue that too much emphasis on the essential dignity could prevent someone making this distinction in the particular cases - for example when it helps rank with trine to the Sun from Aquarius by day, but causes divorce with square to the Moon in a dual sign in a male nativity, Aquarius is not going to help the first and mitigate the latter, I argue that is going to increase and actualize the effects of both.
Powerful Saturn at the nativity does not mean that it will give only very good or very evil at all times (though it certainly can exceed in one direction), if you use the recasting of horoscopes at solar and lunar revolutions, planets change their powers, which allows for differentiation in the chronocratorship. You can't make this important differentiation if you only use primary directions, profections or what have you with the nativity though.
