Better traction with thinner tires. Usually, they weigh less as well. Don't rub as much, and allow for better turning/handling on road.
I have run 235's on all my Rovers for 15 years. The 7.5's are virtually the same, and I think there is a reason the military puts this size on their Rovers.
Project: Aux 110
1965 IIa SWB
1988 Saudi 110 (soon to be 300tdi)