The quick answer is “both”.
Kate asked for a comment to Pluto’s status a week ago, and I figure it deserves a post of its own.
When Pluto was discovered, (February 18, 1930) the astronomers were looking for a much larger body to explain the (still mysterious) perturbations to the orbits of the outer planets, and specifically of Neptune. Something out there is big enough to pull the king of the sea off course in a regular and predictable manner. We still haven’t found it.
In a “rags to riches” scenario, Pluto happened to be in the right place at the right time. The somewhat insignificant dirty snowball achieved the high and lofty position of “planet” and became a star overnight (yes the pun is intended, and no I’m not giving up may day-job to write historic fiction just yet).
Astronomers were mostly happy to add the quirky little guy to the fold of planets, and the astrologers set to work to find out its significance.
To determine the significance of any object in the solar system, astrologers put the object through its paces in thousands of charts to work out what it means for them. (Truth be told, some astrologers do this, the rest of us buy the books and then do our own more limited research.)
By that test, Pluto earned his stripes in the astrological world very quickly. Cycles of roughly 245 years (Pluto’s cycle in the tropical zodiac) appear fairly consistently in history, and transits of Pluto to natal horoscope positions are easily identifiable as huge turning points in the lives of individuals.
No two astrologers practice their art exactly the same way. There are some who use ancient techniques who have no use for Uranus, Neptune, or Pluto at all. There are others who use everything, including various collections of asteroids. There are others who use the 10 regular chart objects and several mythical objects that don’t physically exist as far as we can tell.
Me? I use Sun thru Pluto, one other dirty snowball called Chiron, a couple of significant nodal points, the “horoskopos” (ascendant) and the Medium Coeli (meridian).
Astrologers are far more interested in the fundamental usefulness of an object in the various forms of astrology one might practice, than they are in the scientific classification of solar system objects.
In short, astrology does not rely on astronomy’s classification methods for determining significance.
Pluto’s demotion by astronomers does not diminish its effectiveness as an astrological tool. Astronomy and Astrology are two separate studies that rely on some common information.