@Devil: Well, mostly it's about drawing a line somewhere, because if there would be no limit on amount of traits one can have as long as they add up to 4 traitpoints, there could be additional min-maxing and powergaming by taking all kinds of slightly bad traits and taking good traits in exchange and so on. Also there is for example honest-suspicious combination which gives you +1 intrigue in total, though on the price of being disliked and the main cause for not having all characters with 'em is that it would use up your whole trait limit. Also the disadvantage and advantage of different traits varies on things like whether or not character is a ruler, whether or not he has vassals and so on.