In textual languages, dataflow diagrams are drawn as part of the program design process and then translated into text.
Visual languages omit the translation step.
A constraint may affect many variables, which in turn may affect more. This kind of interaction can benefit from a diagrammatic representation. The solutions is the set of values that satisfy all the constraints simultaneously. The latter is a procedural language using a film-making metaphor. Even though it uses text, in a spreadsheet the relationships between the data and the expression of the computations are represented as part of the form itself, not described textually.