Aesthetics and visual harmony usually go together in web design. Aesthetics in web design should be visually harmonious, without clutter, pleasant, and unified. No web design company would ever release badly cluttered web design in the market and risk losing clients.
There is small difference between aesthetics & visual harmony. Visual clutter, disharmony sometime lead to higher bounce rates and lower engagement. However, visual harmony and considered aesthetics can increase engagement, brand trust, and conversions.
But, also understand that aesthetics aren't everything. They can sometimes backfire, regardless of how beautiful the website is.
One should better understand the target audience.