Surely you think between two charities, one that takes a $1,000 and buys caviar for starving children and one that feeds 1000x as many bread the second one does more good per $ than the first.
Another example I've heard is hospitals asking people to stop skydiving to raise money for them, as the mean cost of medial care the average skydiver needs due to skydiving injuries exceeds the average money raised by skydiving.