What is Public Art and how is it perceived??

The traditional perception of artwork places it in some shape of gallery, surrounding white walls, people all passing in the same directions with the same rhythm and movements; Stop... look... move.... Stop...look...move! But when we remove the walls and place the work in say, a street, what happens then? What does the general public think? Do they appreciate it less? Or more? If its there to just make something look more interesting or to fill in a gap in a wall and does not make any profit, is it worthless?? If it attracts no audience, does this mean it's not really art? Is it still about the quality of the work, the certain type of brush stroke, or is the underlying message more important? Is consumerism taking over the artworld and destroying its substance? Or simply looking at it through an updated perspective? Will any of these questions above have an actual one-sided answer? Or am i going round in circles?