That is the idea of the Princess. She is able to seduce an occupying Knight away from the city, making the Knight unable to score.
Is it very juvenile of me to find that sentence amusing? Maybe lack of sleep is affecting my humour.
Perhaps, but I just re-watched Shrek 2 so I find it amusing too. You can always think of the Princess as a damsel-in-distress, rather than a seductress. Either way, the Knight is distracted away from his duties. Stupid damsels...always getting all in distress...and why don't the "protective" dragons eat the damsels?! I mean, do they really get filled up on the sheer number of Knights coming to rescue the damsel?