Why? Effective Citizenship.
Every day you and I make thousands of decisions. Walk to the store or take the bus. Ride your bike to work or drive you car. Write a blog entry or watch a movie. Go to bed now or in two hours. Each decision is a decision to alter the world in some small (or big) way. To be engaged is a chance to understand your role in the world and thus the consequences of your actions.
Today at lunch I asked where the salmon was from. (Atlantic high in PCB's, Pacific generally considered healthier, farmed more sustainable though with a host of environmental impacts, wild limited in quantity. Wild Alaskan generally considered the Salmon of choice for the ethicist.) The girl did not know. She then recommended to me the lamb burger. My response, "Where is the meat from?" Again did not know but asked the man standing nearby, who coincidently was the restaurant owner. He said his eggs were cage-free but the meat was not free-range. I selected the burger anyways.
Analysis I asked the origin of the fish and meat products for two reasons: to learn the impact of my spending and secondly to indicate to the restaurant that this was something I cared about. How much did I care? Today not enough to stop my purchase but enough to bring up the topic.