What is the significance of the system of checks and balances?

Theoretically, this ensures that no one person or one agency has ultimate power. Unfortunately the system has been so destroyed over the years that many checks and balances are no longer in place.

The constitution was meant to have a balance of strength and flexibility, this is why they need it, so one branch does not have any too much power(said above) so there isn't too much strength in 1 branch and there is flexibility between all the branches.