Well in some cases size matters. You put a cheetah and a tiger against each other and everyone knows who to bet on, cheetahs aren't built to battle really (which sucks because it means the lions can steal all their kills) a leopard and a lion the leopard pretty much has to run for its life precious and climb a tree. However in the case of lions, tigers, and ligers, yeah, the size difference really, really isn't enough to decide anything.