You have to be practical here. If your optimal fight weight is closer to the lower division than it is the higher division, you choose the lower one 10 times out of 10. Yes even if it means dehydrating yourself to shed a few pounds at the weigh-ins. Some take this too far thoughDing, ding, ding, ding! You win the prize! I know why fighters cut weight in regards to weight classes and, you are exactly right, it is to fight smaller competition. Shedding pounds for mobility, however, is an entirely different issue. Dehydrating and starving yourself isn't for performance, that cut is meant to fit into a lower weight class but my buddy, for whom the question was intended, would not answer because it would blast a hole in his argument.