One thing about the balcony scene is that, in one respect, it actually serves to contrast the two characters Romeo and Juliet. We see how very impetuous, irrational, and emotionally driven Romeo is. In contrast, we see that Juliet is much more practical and sensible.
We see Romeo's emotionally driven impetuousness the moment he scales the garden wall in hopes of another glimpse of Juliet. As Juliet herself points out, what he did was very dangerous, as we see in her lines:
How cam'st thou hither, tell me, and wherefore?
The orchard walls are high and hard to climb,
And the place death, considering who thou art,
If any of my kinsmen find thee here. (II.ii.66-69)
Yet, despite being aware that he is putting his life in jeopardy, Romeo refuses to be guided by rational thought and rather lets his intense, passionate emotions be his guide. Since his action of scaling the wall is sudden, rash, and guided by emotions, we can also say it is impetuous. The emotions that guided Romeo were obviously his passion and intense physical attraction for Juliet, which we see him portray in his opening monologue.
In contrast, Juliet proves herself to be much more sensible. She even has the sense to hesitate to exchange voes of undying love with Romeo, seeing that it's far too soon do so, as we see in her lines:
Although I joy in thee,
I have no joy of this contract to-night.
It is too rash, too unadvis'd, too sudden. (122-24)
Hence, the famous balcony scene shows a great contrast between their characters, portraying Romeo as rash and impetuous, while Juliet is the more sensible one.
One of Juliet's most famous lines: "O Romeo, Romeo! Wherefore art thou Romeo?" When Juliet says this, she is not asking where Romeo is. She is asking why he is called a Montague, her family's enemy. She states only his name is her enemy, not the person. She is speaking this to herself, not to be answered.
Once she realizes that Romeo is eavesdropping, she becomes flustered. The love Juliet has for Romeo is not a little crush, she is deeply head-over-heels in love with him. Romeo realizes this while he is eavesdropping, and Juliet is worried because when two people have feelings for eachother, they usually dont tell one another right away.
The lines both reveal that Romeo and Juliet are in love with one another.