First, in order to understand this scene, you must have knowledge of the mythical Phaeton & Phoebus to whom Juliet is referring in the first four lines of 3.2: "Gallop apace, you-fiery footed steeds, / Towards Phoebus' lodging. Such a waggonner / As Pheaeon would whip you to the west / And bring in cloudy night immediately."
Phoebus was the Sun God. His brash young son, Phateon, convinces his father to let him borrow his chariot and drive it around the sun. Phaeton, however, is too inexperienced and lacks the ability to control the incredibily strong horses. The chariot runs wild without an appropriate helmsman, comes too near the earth, burning up towns & innocent people.
That Juliet does not realize Romeo's similiarities to the immature Phaeton & instead lauds him is ironic.
The following lines in this scence continue to reveal the immaturity of the young lovers. In lines 7-10, Juliet argues, "Lovers can see to do their amorous rites / By their own beauties; or, if love be blind,, / It best agrees with night." People with some experience in the world, know that the light of infatuation is short-lived & that no good comes of going into anything blindly.
The concluding lines further reinforce Juliet's starry-eyed romanticism (21-22) "Give me my Romeo; and when I shall die / Take him and cut him out in little stars...". By lines 30-31, Juliet discars all reason, calling herself an "impatient child that hath new robes / And may not wear them."