Here is the question that Iris asked on this site: Could you say a bit about how you would distinguish the cutting away of the unnecessary by Saturn from the letting go of the unnecessary by Pluto? How might they feel different?
Iris is right: both of these planets bring loss and even death. Saturn is personified sometimes as the Grim Reaper himself and Pluto is indeed Lord of the Underworld, King of Hell. But although they both bring about endings, the quality of the energy is quite different.
If a person comes into your life under a Saturn transit, he is likely to be a wise, older person, a counsellor, a parent figure, a teacher, even an astrologer; he may be cold and old and settled in his ways, but he is unlikely to wish to harm you as long as you play by his rules (although his rules can be stifling). His main rule is work at it. A Saturn transit well-handled can be profoundly satisfying.
If a Pluto person comes into your life, she may be a sadist, emotionally or even physically; violent, cruel, irrational; brutally honest. Pluto might want to hurt you or use you. Sometimes, you just don't know what Pluto wants because the game she plays is far bigger than you can imagine. Mainly Pluto wants you to see the truth however difficult. A Pluto transit well-handled can be exhilarating, cleansing but almost never without some pain.
So you can see already how the energy is not the same.
With Saturn transits you are often given a choice: stay or go, break or build, embrace your responsibility or run away from it. You reap the consequences – often surprisingly quickly but sometimes over a lifetime.
Saturn transits are not as bad as they are painted. But you have to be willing to do your duty.
Let me give you a clear example from my own life. When my first child was born Saturn was on my Moon, which is the planet of motherhood, and also your own inner child. Now if you read the textbooks, they'll tell you that transit is about depression or feeling lonely or emotional loss.
In fact, it was about my becoming a mother. The child in me became a mother in that moment - and because I was ready, my experience was euphoric and joyful. I stepped into motherhood wholeheartedly and grabbed the responsibility that was offered. Saturn rewarded me handsomely. This was a harvest. I had waited a long time (Saturn) to have children and the time was ripe.
Saturn likes patience.
Sometimes it is hard to sort out transits anyway. For example, the 1950s Saturn in Libra lot had Pluto transiting Saturn on their last Saturn Return, so how can they really be sure what is Saturn and what is Pluto?
Pluto is more ruthless than Saturn. Because he is so far out in the Solar system, he is even more impersonal. A Pluto transit can feel like a deus ex machina has just walked into your life and skewered you with his light sabre.
Something ugly or inconvenient is often revealed. Secrets and lies come out. Pluto deals with the truth but often seems to take a bitter pleasure in the more unpleasant truths. For example, the scandal of paedophilia in the Church came out under Pluto's transit of Sagittarius (organised religion).
My last big Pluto transit was an opposition to my Moon. My grandmother died and my relationship with my mother was changed as a consequence. A veil was torn away and I suddenly saw things much more clearly. It wasn't nice, and I don't think I handled it as well as I should.
For a good Pluto transit I give you my friend L, who had Pluto squaring her Sun about 10 years ago now. She's an astrologer and so she booked herself in for deep healing of a very intense sort. She knew she would be transformed somehow so she went the whole hog. She looks back at that transit with gratitude, a time when she really understood herself (Sun) very deeply.
I could actually write a book, but I hope that gives you a feel for the difference.