> [...] and never understood what use they were to anyone.

Different people consume data in different ways. For some, data is easier to understand when arranged in tables, black on white, as they can skim through a lot of datasets quite easily.

Others benefit by a colorful, graphical representation, which Sankey provides.

From my experience in consumer facing applications, I'd assume that a colorful, flashy, nice-looking Sankey could boost sales. People prefer things that look nice.

Well, I'm considering purchasing Monarch because of this feature, so not sure that's true. I am a visual learner, but the reason I like them is they help me at a glance see the flow of money through multiple categories. Some systems represent this as pie charts you drill down on, but a Sankey shows it all at once glance. As far as actionable insight, they help decide areas that would be most beneficial to reduce expenses or increase revenue.