This is a great write up of why Casablanca is an immaculate screenplay: economy of vision. Great architecture doesn't need a thousand beams but just a few, perfectly placed arches. Picasso could draw a single line and capture more than the thousand lines of a poorer artist.
In Casablanca, there are no unnecessary scenes: every single scene has one or more uses in terms of plot. As they say here, Yvonne's a background character found in three small scenes and when we see her in her third and final scene, joining in 'La Marseillaise' it's like a gut punch so hard that it takes my breath away -- every time I see it.
This is what you can do with storytelling. These are the heights we can reach.