Tiny Tim performs a very important function in the short story, A Christmas Carol. He is the one who shows Scrooge in Present time (through which Scrooge is ushered by the Ghost of Christmas Present) the effect of Scrooge's stinginess on those around him.
Scrooge can see the effect on Bob and his family of the poor wages he pays Bob Crachit. Ill, weak, feeble and walking with a crutch, he will soon die. Scrooge asks if there is any help for such a boy and his own earlier words are turned against him by the Spirit of Christmas Present:
"What then? If he be like to die, he had better do it, and decrease the surplus population."
Scrooge hung his head to hear his own words quoted by the Spirit, and was overcome with penitence and grief.
Scrooge now understands what the effects are on the whole family when he pays his help, Bob Cratchit, so poorly. Tiny Tim illustrates for the reader what the difference is between greediness and kindness. The story is timeless, and it is so partly because this question is still relevant today.