Keeping the light source consistent is elemental in this particular painting. Shadows will always improve a composition in nearly all of your paintings.
Notice the shadow on the building and the pavement. The light draws across both in a similar way. The focus is on the building, so features on it are drawn in much more detail. The shadow from the wall is meant to lead your eye down the street to the paintings subject.
Putting in shadows under the balcony in the same relation to the shadow cast by the wall is essential. Especially for subjects which have only one light source.