The link talks about philosophies, but they can be...
art is technically useful
Art - The expression or application of human creative skill and imagination, typically in a visual form such as painting or sculpture, producing works to be appreciated primarily for their beauty or emotional power. We are talking about the typical form of arts, which is painting or sculpturing. ' It was painters and sculptors who allowed us greater understanding of geometry, symmetry, and construction.' Yes but geometry, symmetry, construction etc are now studied in Math. Would they qualify as art. Also building a house would require usage of all 3 skills as well. Art doesn't have a practical use, it just beautifies things. The link talks about philosophies, but they can be expressed through writings. Emotion practically doesn't have a use unless its good, and even then emotions expressed through art won't impact the watcher. Yet I don't see why paintings are still sold at ridiculous prices.