I suppose also I should elaborate a little on the good and bad of this one instance for you I forgot this may answer your question more. However remember we are all different so there is no one size fits all.
Ok so Neptune is coruling my chart cause of intercepted Pisces first house.
At first the person kind of got me into a bad situation with drugs and people that were in that lifestyle (ruled by neptune) however both of us were on a low Vibration at that time I also kind of got her back into it I admit I am sure that was this aspect. I started getting spiritually attacked by entities that were attacking her. This is the classic Saturn Neptune type stuff here.
However after awhile since we are both working on a positive life and meditation and stuff nothing negative is happening anymore we both also helped eachother out of all these things too. So in the past year or two it's more been like the person tries to find structure (Saturn) where I have my dreams and spiritual ideals. It's not bad anymore. This is why I say it depends on the vibration of the person.
If neither people meditated I can see Saturn in hard aspect to co-ruler/main ruler being a complete nightmare for both people like Pythia said. I think that she was speaking more for general public in some of these things than two people that meditate. In fact I think if both people are mature and at a high enough level anything just about with astrology may be able to be smoothed out. I know someone still won't want to hang around a lot someone who has terrible synastry with them that makes sense but I mean a few aspects like this it is possible if some or the rest of the chart is positive to still be good friends and help eachother.