Playwrights use stage directions to give more insight into how the characters should be interacting with each other. Shakespeare uses actually very few stage directions compared to some modern playwrights who detail every move a character is supposed to make.
Stage directions help develop the plot because they help the actors and audience physically move in the space to move the action forward. For example, in Caesar we get the stage direction "<span>CASCA first, then the other Conspirators and BRUTUS stab CAESAR". We understand through the dialogue that they are going to stab Caesar, but this gives us the person who stabs first and the person who stabs last. This helps give meaning to the characters because we learn a lot about Casca (he is the most willing to start the violence) and Brutus (he is still hesitating and it takes him the longest to actually be able to follow through). Also, it develops the plot in the obvious way that if this action does not occur, the rest of the play could not happen.</span>
<span>Odysseus is a generous leader.</span>
