Benefits of gold/silver coins over bullion?

I have heard that the development of money in Lydia in the first millennium BC was a major development in history. How so? What major benefit would any society have if it used gold and silver coins in everyday transactions, compared to small gold and silver bars? I'm thinking about the ancient societies where money was developed, not about modern times.

Public Comments

1. Coins were more or less standardized, minted by some authority. Both buyer and seller knew the value of a certain coin. Bars and ingots are an unknown. Weight, purity, etc. Anyone could forge bars of gold/copper mix with lowered value.
2. Bullion bars were a bit big and heavy to carry around in your toga pocket.