Codes of conduct are sets of rules put in place by organisations to establish exactly what is and is not acceptable by their employees. While they do have the advantage of making it clear to employees exactly what is expected of them, they have a few distinct disadvantages, most notably the fact that they need to be both vague and specific at the same time.
One major problem with a code of conduct is that it needs to take subjective ideals and make them objective. Indeed, this is their entire objective point--to take away subjective judgment and replace it with a set, universal series of ideals. However, subjective judgment is an important part of management. The ability to make decisions based on the available information is a manager's best quality. A code of conduct replaces that ability with a set of rules.
A code of conduct needs to be routinely enforced in order to be effective. However, this is at odds with the point above--managers need autonomy in order to do their jobs. So, a code of conduct in a large organisation can either render managers impotent or render itself impotent through vagueness. The two cannot coexist, which is a major disadvantage.
The above two points lead codes of conduct in one direction: vagueness. In order to apply to everyone, a code of conduct needs to be vague. This means that the individual rules tend to be up to managerial interpretation. This in turn means that the organisation is being run by managers anyway. So, it's a catch-22--if a code of conduct is specific, it is unenforceable. If it is vague, it is enforceable, but subject to so much interpretation that it may as well not exist.