Well, what I've seen so far is that some scenes wouldn't appear altogether if I don't meet the required ap/cp.
I haven't checked all the requirements in awhile, but from my memory I'll try and give you some more info.
I would add that affection points really matter only up to around 15-18 AP for some of the companions. I think the highest scene requirement with a companion is 18 AP, unless it's been changed, but that is an outlier not the norm. Scene requirements are usually a lot less for AP, or not required at all. If you want you can always use the RPGM save editor. I posted it some pages back. Just up all the companions AP variables when you get them. So you don't have to worry about it. Won't cause problems for your saves either.
Corruption primarily gives more descriptive/lewd variants to sex scenes. It rarely acts like AP unlocking scenes. However for the endgame, certain characters like Ruksana, Clawyn, and Meredith need corruption points between 10-15 to stay with the player if you choose the evil ending. (I don't think that's changed). Also the flavor text/random companion dialogue, will change during the game depending on a characters corruption. It's more noticeable with Meredith, Ruksana, and Clawyn.
Morality points help dictate getting two companions Carys and Xyless. Carys hates evil players and simply wont join them if their morality is too low. Xyless prefers less than 15 morality. In Redknight's walkthrough you'll notice they state she can only be recruited by more evil players. With the morality requirement I mentioned earlier. However, what Redknight doesn't mention in the walkthrough, is even if you have a high morality, and you choose to enslave her, you can recruit her into your party. (As she doesn't have a choice being a slave). I've never actually played a character where I let Xyless be free. So I assume that the morality recruitment requirement for her is tied to her free path not her slave path. Also you can get one of the better swords in the game, Aetherius, if you have high morality.