The beauty of your design buys you credibility in the mind of a new viewer. If you’re the most talented scientist in the world, but you’re missing one of your front teeth, it’s going to take an incredible amount of effort before people take you seriously.
Along the same lines, if you’re starting a new business, and you don’t have a beautiful brand, website, photography, and emails, it’s going to be much more difficult to establish trust and credibility with your customers. It will also take much, much longer.
This is a great advantage to beautiful and aesthetically-pleasing interfaces, logos, photos, and all designs.
There is also the usability of an interface and effectiveness of a design to communicate the idea that needs to be shared with the customer.
Any of us can start a pizza business. The pizza must be excellent. But none of your new customers will trust that the pizza will be good if the presentation is garbage.
The best pizza on earth would taste worse if it was served in a black plastic bag rather than a beautifully designed box. Your beautiful design work will open new customers that good pizza that they would never have bothered to try otherwise.