Say I'm shooting a product on a white backdrop and the client want's it to look like it is surrounded fully by pure white, no drop shadow. In the old days, I'd make a selection around the object, invert the selection, and fill the backdrop with a 255/255/255 tone. Done.
Now the client wants an actual 'clipping path'. So I take the pen tool, click and drag all the way around the object, making full use of the pen tool's bezier curve ability, and make a complete path around the object. Now what? What do I do to make it a clipping path? Do I still fill the backdrop to 255/255/255?