To Prevent Abuse
Its most critical purpose is to prevent misuse of power. If there is too much power in the hands of the President, it can lead to abuse. During the Roman times, some Emperors wielded so much power they endangered the Empire itself.
The history of Europe from the 14th to 17th centuries is replete with stories of monarchs who abused power. The 20th century is filled with examples too, not the least of which are Adolf Hitler and Josef Stalin. Under their reign, millions of people died.
By limiting the power of the Presidency, abuses can be kept to a minimum or completely eliminated. In elucidating the need for separation of powers, this is one of the frequent explanations given.
To Provide Balance
The system of checks and balances is also critical. Consider the following scenario: the President asks that a bill be passed into law. The Congress and Senate approve it. If the Supreme Court did not exist, no one will be able to question its legality. But if there is a court of last resort, anyone can question its validity.
Another example would be when the President insists on spending a certain amount for a given project. If Congress did not have the power of the purse, no one will be able to question the President’s decision. The need for separation of powers can be illustrated in this example too: if the President decides to go to war, he / she must get the approval of Congress. Congressmen and Senators being representatives of the people, they can speak for the masses.
Limit and Expose Corruption
Almost everyday we hear politicians delivering speeches detailing corrupt practices of the current administration. Without the right balance of power, the layman won’t know what is happening.
Granted, some of the issues raised can be biased or prejudiced towards certain parties. But the alternative is worse. At least people will know the issue and decide whether to believe it or not. In countries ruled by tyrants, the common man doesn’t know how the tax money is being spent. In this regard, need for separation of powers becomes evident.
To Ease Management of a Country
Another more practical reason is to make it easier to run the nation. If it was all up to the President, the tasks can be overwhelming. By dividing the duties into the executive, legislative and judiciary governance becomes more efficient.
During the Middle Ages in Europe, power was concentrated in the hands of a king or a handful of advisors. By not designating tasks, managing or running a country became very difficult. In democratic societies, people will know who to turn to.
The need for separation of powers should be understood if only to make sure it doesn’t slip away. Without this system, it becomes impossible for the people to express their will.