What exactly is the director trying to express in the scene where Mia and Sebastian are flying through the stars?

Question

In the movie La La Land, in the scene (somewhere in the middle of the film) where both Ryan and Emma are shown flying through the stars and galaxies.

What exactly is director Damien Chazelle trying to express?

I have a tad idea about it but would like to know more from you guys.

Answer 1

According to a recent IndieWIRE interview with Damien Chazelle by Anne Thompson for Thompson on the Oscars, it was inspired by Mary Poppins:

Next up, the La La Land crew are off to Paris to show the movie to Michel Legrand, who wrote all the Jacques Demy music. They got a kick out of meeting Mary Poppins songwriter Richard M. Sherman. That sequence of the couple dancing above the clouds against the starry sky? It’s right out of Mary Poppins.

Answer 2

It is the cinematic realization of figures of speech for falling in love such as lighthearted and head in the clouds and in their own (beautiful) world.