Chacun puts the emphasis on the fact that each member of a group is part of the action.
Examples
Chacun sait maintenant ce qu' il doit faire.
(Each and) Everybody now knows, what to do.
Je l' ai expliqué à chacun.
I have explained it to everyone.
Chacun peut faire ce qu' il veut.
Everybody can do, what he wants.
Chacun cannot be used, if each member of the group could be part of the action, but is not necessarily also affected by the action. However, in English we also differentiate here, we always have the difference between every and any.
Examples
Tu peux demander
à n'
importe qui, ils te diront tous
la même chose.
You can ask anyone, they all tell you the same thing.
