These threads always crack me up. Yours is a reasonable question I think. Why bother pumping premium if you are only borrowing the car for a few years?
I think the answer likely is that if you perceive no performance drop off on your leased car, don't bother. I buy cars outright and tend to drive them for awhile. So I use premium. As many like to chime in, why not pay the few extra bucks per tank. Do I really need to? I'm not really sure frankly. I do as much out of habit as anything else.
But I don't think you are necessarily being cheap not to do so on a leased car.
Flame away premium snobs.