Let it bleed--the duality of a character
Just a theory:
This scene, a brief moment during the last heist, where De Niro's character tells the bank Manager to "let it bleed", referring to the manager's busted nose, reveals the duality of De Niro's character, and reinforces the main themes of the film.
One might perceive this scene as one which displays the heartlessness of De Niro's character, but this is not wholly true. In a way, he was doing the bank manager a favor. (Stick with me)
On the one hand, "Let it bleed!" So that all those terrified people in the bank can see him/bleeding and continue to be terrified.
On the other hand, bleeding is a natural and necessary healing agent for wounds (though the assistance of bandages would of course be preferable and a definite benefit).
The scene opens with De Niro's character actually pleading to the bank's occupants--"DONT BE A HERO, we're here for the banks money, etc.". What he really means is: don't make me hurt you. (Not cool)
He tells the bank manager to let it bleed because this will allow the wound to heal more efficiently, but this action also serves as a deterrent to the other hostages in the bank. However, he did punch the guy in the face to begin with, so not really a fruitful gesture, but a gesture all the same.
This film is a great morality tale.