Why does that make a difference? If I've got nine cards - three rock, two grain, three sheep (which I gain on a regular basis) and one brick (which is a difficult commodity for me to get hold of) then it's definitely in my interest to get to the seven-card safety limit, because otherwise I will lose a vital city-building resource or a rare brick resource. The loss if I roll a 7 is high. The loss if I trade down is low. It's even worse if I hold eight cards - the city building materials and three sheep - because then I definitely lose the ability to build a city if the bandit is rolled. Here it certainly makes sense to trade two sheep for one to protect those resources - I definitely lose a resource by doing so, but if the bandit strikes I lose four resources and worse, I set my building back by a turn, which could lose me even more in missed opportunity. Again, that becomes more significant in Cities & Knights.