What are  advantages and disadvantages of absolute monarchy

All advantages of an absolute monarchy go to the monarchist. All the disadvantages go to the subjects. 

You must understand how monarchist think. In a monarchy, the King or Queen has been chosen by God to be the rule of the lesser people. The King or Queen is given the God Given Right to do so. 

The advantages of an absolute monarchy are that all subjects are subservient to the royal throne. All laws, & orders are legitimized by God, and therefore not a mistake. The subjects must do as they are told.

"In my First Treatise of Government I showed these four things: (1) That Adam did not have, whether by natural right as a father or through a •positive gift from God, any such authority over his children or over the world as has been claimed. (2) That if even he had, his heirs would not have the same right. (3) That if the right were to be passed on to his heirs, it would be indeterminate who were his heirs, because there is no law of nature or •positive law of God that settles this question in every possible case; so it wouldn’t be determinate who inherited the right and thus was entitled to rule. (4) Even if all that had been ·theoretically· determined, ·it would be useless in practice·: the knowledge of the chain of heirs running back to Adam has been utterly lost, so that nobody in all the races of mankind and families of the world would have the slightest claim to have that ·supposed· right of inheritance. All these premises having, as I think, been clearly established, no rulers now on earth can derive the faintest shadow of authority from the supposed source of all ·human political· power, Adam’s private dominion and paternal rule. So if you don’t want to •give reason to think that all government in the world is the product purely of force and violence, and men live together only by the same rules as the lower animals, where strength settles every issue, and so •lay a foundation for perpetual disorder and mischief, riots, sedition and rebellion (things that the followers of that ·‘force and violence’· hypothesis so loudly cry out against), you will have to find another account of the beginnings of government, another source for political power, and another way of settling who the people are who ·ought to· have it—other, that is, than what Sir Robert Filmer has taught us" John Locke, Second Treatise of Goverment

The disadvantages of an absolute monarchy are that the people have no assertion to protect their rights, such as a Magna Carta, and are at no Liberty to make any amendments to their government. 

Because broadest terms allows the law flexibility depending on changing society and circumstances.