Authors firstly write from a point of view based on their own preferences usually. It's not going to really lay it out because it's really dependent on each theme in each person's natal chart, and what happens when its synthesized. Jewel with Truth In Aspect Astrology is a great synastry astrologer: https://www.youtube.com/channel/UCZW2APnsyyVHrh_NK4FCavQ
If you click on her most viewed videos, there are some that answer general questions like yours.
- You don't necessarily want too many of any type of aspect.
- Chart rulers and themes are important. For example, I've personally noticed that people with a lot of fire/air, or squares in their own chart like the more "difficult" aspects and won't settle for someone who they have too many flowing, calm aspects with.
-Where is the person at in life? Some people are convinced all they want is physical intimacy and some want long-term. Is this also referring to platonic, work, or romantic relationships?
Moon is paramount. I find Moon/Venus, Moon/Mercury, Mercury/Mercury to be pretty important. Saturn will show commitment and is nice to have with Sun & Venus in harmonious (trine, sextile) in my experience. Someone's Saturn conjunct/opposite your moon could feel suffocating and I'm not a fan, but if a person is really Saturnian they might like this if the other aspects are light. Jupiter also lightens up heavy connections and I really even hard aspects with Jupiter.. I'm very Jupiterian though so might not apply to everybody. These are just examples.
Bottom line is it's good to have variation and supportive aspects that are congruent with the themes in your own chart.