Why are checks and balances and separation of powers necessary?

They are important because without them there would be chaos. Checks and balances is basically checking on the others. The separation is for the three branches (Executive, Legislative, Judiciary), each have the power to do their own duty; so there would not be just ONE person who takes over.

Answer: checks and balances let each branch of government not gain too much power over the other, separation of powers has the same concept so not one individual or one group has all the power to make all the choices. They all work together and if someone over steps checks and balances are there to ensure order