Revenge is sweet and not fattening- Alfred Hitchcock

Revenge is a double edged sword.
It is a gun that when you fire it, it kills you too.
Revenge is the poison that heals you only to stick a dagger through your heart.

When Alfred Hitchcock said that revenge is sweet and not fattening, he was remarking on how the pleasurable things in life often are bad for you.  He also was saying that revenge often makes you feel better, at least initially.
When asked if revenge ever makes sense, I automatically want to say no simply because I know revenge is never a "good" thing. However, that does not answer the question of whether one ever should engage in revenge. Revenge will always make sense to the person seeking it. No one wakes up one morning and decides to go shoot up a school because it feels wrong.  Every act is performed in the moment and it will always feel right when committed. Everyone has done something and then regretted it and wished that it had never been done. But they still did do it, and when they did it, it seemed like the right thing to do. So revenge does make sense at the moment, but then it so often comes back to cause more harm to the person who acted vengefully; it is "to stick a dagger through your heart."
However, just because revenge makes sense at the moment does not mean that revenge is ever justifiable or right. Hamlet wants to revenge his father's murder, to him doing whatever it takes to avenge that death would seem like it is his moral obligation. However, killing the innocent in order to punish the guilty is a moral sin. Had the play ended differently and had Hamlet not died, his actions would have caught up to him and he would be miserable for the rest of his life.