What is the advantage for Hillary Clinton to giving up her delegates now?

Why is it important that Hillary Clinton has to withdraw from the race? I understand that she is vying for the VP position. However, why is the act of withdrawing necessary, in light of the fact that she lost? I heard that it had something to do with recouping her costs, but I dont understand what one has to do with the other?

Public Comments

1. The quicker that the party unites behind Obama, the better chances they will have in defeating their opponent in the election. Time is short, the stakes are high and much is to be gained or lost in this election.
2. She weakened her bargaining position for VP by leaving her withdrawal too late in the game....just be glad that with so little savvy of politics she didn't end up as president....