Athenian democracy was created as a way to give common people a say in the running of government. What would be some advantages of a Democratic system compared to a system where a king had total control? what would be some disadvantages?

The issue with democratic systems versus a republic or a constitutional monarchy, whereas there is a Magna Carta, or otherwise any guaranteed protection of the people's rights is that it can be voted away to a majority.

An unelected king that has total control over his subjects with no restraint of power or protection for the people will make none the difference but that in a democracy that person was elected to have total control over his subjects.

The disadvantage, or advantage, of a democracy, is that the majority will always rule over the minority. Regardless of there protected rights.