Compatibility is about relationship durability; the “glue” that either makes it easy or, by lack thereof, difficult for a relationship to persist.
In a sense this talks about the good/bad of the relationship because durability is quite an important factor of any good relationship. And in a durable relationship, love is an investment that can prosper and multiply. But durability is not the sole factor of what a relationship actually feels like.
Take a person with a hypothetical birth chart that shows terrible relationships. That person can meet someone with whom they are very “compatible.” The result? A long lasting horrible relationship.
This is a simplified example of course, to get the basic point across. Real world cases are more complex. People have all sorts of conflicting karmas happening almost at once in their lives. We have 18 things giving so many different varieties of good relationship karmas, and 4 things giving so many different types of negative relationship karmas – and these things come to the fore at different moments in our life depending on the astrological cycles and whatnot. So at one stage in our life, meeting a person with whom we are highly compatible creates a very good relationship. At another stage – when a different karma is bearing fruit due to our astrological cycles – the same level of compatibility in a relationship causes a lousy, painful experience that is difficult to break off.