Why have Constitutions, Laws and Regulations? I know that it's a theme I keep coming back to - but it is worth repeating -
"Power tends to corrupt,
Absolute Power corrupts absolutely"
Experience tells us that without effective constraints - power WILL be abused - whether it is the petty official or the great dictator. That suggests that two principles need to be adhered to -
1 the costs of breaking constitutional (and other) rules need to be greater than the advantage that can be gained through disregard of them. That cost may be in the form of legal sanctions. A President of the United States "shall be removed from office" when he has been impeached and convicted of "Treason, Bribery, or other high Crimes and Misdemeanors"; a breach of electoral law can lead to the election being declared void - which is the reason why there was a recent by-election in Oldham East and Saddleworth (for more information press here). In Britain we may rely more on "conventions" rather than legal rules - but they still work on the principle that the cost of breaking the convention is greater than the short term advantage.
2 there should be limits on the discretion of officials. Dicey was opposed to granting wide discretionary powers because he believed that it would lead to arbitrary decisions. In the modern state, that may be unworkable. The English Courts have responded to modern needs by developing the remedy of "Judicial Review" which allows the Courts to oversee the use of discretion by public bodies and others exercising public (as opposed to private) functions.