A couple of months ago we met with a prospective client to discuss their use cases and conduct requirements gathering. They really liked what we showed them, but the CFO wanted a dashboard that displayed the data in the app in a specific way. We shook hands, told them we would contact them soon, and parted ways. It was around 9 AM when we stepped outside the client's office and got back in our cars.
By 5 PM that evening, we had a stunning, fully functional dashboard built and deployed to the demo environment. It utilized a few new database tables that aggregated data, some data processing done by Elixir, passing that data to the Vue front-end and displaying it using Charts.js and a few other UI libraries.
I sent a quick email to the CFO with the URL. He responded ten minutes later with, "holy cow, why didn't you show this during our meeting if you had it already?!" :)
We are meeting with them again later this month, hopefully to sign them on as a client.
(For reference, I've used Rails and ASP.NET with C# before Elixir, along with JQuery back in the day, and then a bit of React. Can't speak about other frameworks and languages.)