One effect of the stage directions is that the reader has an opportunity to interpret characters' actions that are described but not addressed aloud, and these actions or descriptions of the tone in which certain lines are to be spoken sometimes tell us even more than the words themselves. They allow us to understand more fully what characters are thinking and feeling in moments when they may not be saying everything aloud or telling the whole truth. For example, in Act II, the opening stage direction tells us that John Proctor seasons the stew his wife has prepared while she is out of the room. When she serves him, stage direction tells us that "She sits and watches him taste it." This helps us to understand that his response to her cooking is important to her, so important that she watches for his reaction when he tries it. She is anxious. Further, he tells her that "It's well seasoned." Now, we, the audience, know that he's not being entirely truthful: he adding seasoning to it, so he must not have found it well-seasoned to begin with; however, he now compliments his wife on the stew when we know that he was "not quite pleased" with it as she'd prepared it. This is a man who's willing to tell a small lie if he thinks the reason is good; readers know this because of stage direction.
A moment later, Proctor tells his wife that he "means to please [her]," but when he tries to kiss her, she only "receives it" and, "With a certain disappointment, he returns to the table." With only their words and no stage direction, readers would be much less likely to pick up on the tension in this relationship. The words themselves are, for the most part, all good, kind, typical of a loving relationship, but the actions betray the sense that not all his well between these two people.