Think of your favourite football, basketball or hockey team. You love them as a whole don't you? Because they form a team, and because the sum of their talents is greater than their isolated individual performances. However, if you look closely at your number one team, you'll notice that not all of the team members contribute in the same way to scoring goals.
Now think of your favourite team's players as individual pages of a website. Wouldn't you be interested in knowing what player makes the highest amount of assists, the highest number of contributions to scoring goals? Much in the same way as a performance chart would help a coach spot his most valuable players, Google Analytics uses Page Value to let you know which page is contributing the most to your website's sales funnel.