To deliver an opinion, is the right of all men; that of constituents is a weighty and respectable opinion, which a representative ought always to rejoice to hear; and which he ought always most seriously to consider. But authoritative instructions; mandates issued, which the member is bound blindly and implicitly to obey, to vote, and to argue for, though contrary to the clearest conviction of his judgment and conscience,--these are things utterly unknown to the laws of this land, and which arise from a fundamental mistake of the whole order and tenor of our constitution.
Parliament is not a congress of ambassadors from different and hostile interests; which interests each must maintain, as an agent and advocate, against other agents and advocates; but parliament is a deliberative assembly of one nation, with one interest, that of the whole; where, not local purposes, not local prejudices, ought to guide, but the general good, resulting from the general reason of the whole. You choose a member indeed; but when you have chosen him, he is not member of Bristol, but he is a member of parliament. If the local constituent should have an interest, or should form an hasty opinion, evidently opposite to the real good of the rest of the community, the member for that place ought to be as far, as any other, from any endeavour to give it effect. I beg pardon for saying so much on this subject. I have been unwillingly drawn into it; but I shall ever use a respectful frankness of communication with you. Your faithful friend, your devoted servant, I shall be to the end of my life: a flatterer you do not wish for.
One of my favorite speeches, I wish the elected officials for local office had the balls this man had or pretend to have them. By voting for someone, you are trusting their judgment to do what is best, for you and your country. We often forget that last part. WHAT IS BEST FOR YOUR COUNTRY. Sometimes, your interests simply aren't aligned, we all need to remember that.
Source: http://press-pubs.uchicago.edu/founders/documents/v1ch13s7.html