The Constitution was written to seperate and restrict the powers of government, thereby safeguarding the rights of individuals. Those who would argue that it makes the government less "efficient" miss the point of the document's intent.
Constitutional restrictions were often intended precisely to make government less efficient, which might not be a bad thing. For example, the government would operate much more "efficiently" if it could exercise "eminent domain" in an unrestricted fashion, but such efficiency would come at the price of a loss of individual freedom and property rights.
I agree with the posters. It seems that the way that the Constitution is written, too many loops holes and individual interpretations are allowed to be made in order to serve those who are trying to support or negate specific ideas/laws. The Constitution is simply a tool used by people/groups in opposition. For me, it should never be used as a tool.
Of course, we need to remember that the Constitution does have a number of benefits, but certainly the way that it presents the US law making bodies with a series of barriers or hoops that need to be jumped through can be rather frustrating because of the time it takes to pass new laws.
Another example is that the Constitution makes the president the commander in chief of the military. But Congress has the responsibility for funding the military, which is a sword it holds over the executive branch. Yes another example is that the president selects nominees to the federal courts, but only with the "advice and consent" of the Senate.
In addition to the post above, which I agree with, there are a myriad of ways in which a bill can be rejected or tabled, and only one way in which it can be passed. This allows a minority of elected officials to prevent votes on bills the majority would support. Some call this the Tyranny of the Minority. There is a purpose to having such a cumbersome and slow process, in that it sometimes forces compromise in order to achieve anything, which represents a wider group of people.
Another place to look for examples of your thesis is in the judicial system. There are many constitutional restrictions on which courts hear which kinds of cases and on the various policies and requirements for appeal which a can make the system less than efficient, but are in place to protect the both prosecution and the defence in legal dealings.
In the US, at least, they do it by making it hard to make laws. The Republicans think, for example, that they have all the answers to our current crisis. But they can't enact them because they only control the House, not the Senate or the White House. This separation of powers makes it very hard for either party to enact its agenda. That makes the government less efficient and less effective.