Each other person shows not only their opinion of me, but also my opinion of them. I know that their opinion of me is important in all kinds of ways, but what is my opinion of them for?
For example, my wife likes me well enough, but I don't like her much:
Does that impact the chance of having children, maybe? If so, it doesn't seem like it has much of an impact, since we've already had two children after not many years.
And as far as I know there's no way to switch your character aside from death*, so it's not as if the opinion your current character has will matter after you take control of your heir. I suppose it can indicate incompatibilities between me and other people that might flag problems I should deal with. Does it matter otherwise?
* During normal play, I mean. I know I can save and load as someone else, but the sort-of cheat of switching to NPCs to manipulate the state of a savegame doesn't interest me. I'm only interested in the opinion's relevance, if any, to actual game mechanics.