In Act II, Scene 2, Romeo first speaks softly to himself in an aside because he is excited to hear Juliet's voice, and in the second aside, line 37, he is uncomfortable because he feels that he is invading Juliet's privacy by standing beneath her balcony and hearing her private thoughts. But, by not speaking, he hears more.
Romeo says, "Shall I hear more, or shall I speak at this?" but he decides that it is better not to speak. This aside is effective because by keeping quiet, Romeo learns that Juliet shares his loving interest and wants to be with him as he hears her say,
....Romeo, doff thy name,
And for thy name, which is not part of thee,
Take all myself. (2.2.47-49)
Learning of Juliet's love, Romeo then becomes emboldened to declare his own desire and love for Juliet, and by so doing, he and Juliet communicate their feelings early on. Otherwise, they would not know so soon how the other feels, and might have difficulty in contacting each other since their families are enemies. Certainly, this Scene 2 as it is written enables the drama to advance more quickly than it would if Romeo were to not speak up right away.