Heavier but less bulky, especially if you were transporting funds between countries. Gold and Silver coins are assessed at the face value on the coin which is always much less than the precious metal value. I confirmed that with customs a few years ago when the currency police were stopping people on the boarding ramp to the plane.

@Surfpirate isn't that because the coins are made with more materials than purely silver or gold?

@memorylikeasieve bullion coins are 99.99% pure gold or silver metal for gold and silver coins respectively. Old silver coins were usually 90% silver up until the mid 60's, then they dropped to 40% and then 0% after the mid 70's when America came off the gold standard completely.