I mean post approval, in the RP itself. People simply won't be RPing out specific conflicts (especially if there is a chance for there to be a tangible negative effect) and don't technically disagree with their Servant/Master in any significant way.
I feel like the larger issue at play would be Player/Player friction, rather then actual IC incompatibility of characters (e.g players who just don't mesh well, but are matched together regardless). IC backstabbing and betrayal are about as likely to happen either way, honestly (its just that it ends up being a more impulsive action with randomized pairs).And unlike pre-determined pairs, randomized pairs are "natural" in their interactions as they cannot expect everything to go smoothly. You're dealing with another being there, and backstabbing or betrayal has a chance of happening unless you find a common ground. RP-ing that Master/Servant relationship becomes an actual point, rather than something you can just plan ahead and present to me with bullet points.
I feel that in the end we might up with honestly no interesting character conflicts (especially since its much harder to improvise a relationship that interestingly meshes in some way, and people might just choose to go with the very standard Master-Servant relationship we so often see in RPs).
This I can agree with.Also, it effectively prevents players from creating "super-combos" where Master's and Servant's abilities mesh just perfectly to create game-breaking effects. I know some of you will try that.
I think that it can be curbed by balancing, but it is obviously an annoyance and somewhat tedious issue, which is a strong argument for randomized pairs.