Conversion rate, positive emotions after the visit, as well as the overall impression of your product or service in General.
Let's look at a small example:
Let's say you sell something, you already have a website and you spend for example$200 on its advertising. At the end of the month, you get 20 sales of a conditional product or service. But your site is already outdated both functionally and in terms of design, and it is simply not convenient for users. Consequently, the conversion rate (namely, the conversion of site visitors to real customers) will be low from 1% to 4%. We are developing a new website for you on all marketing eve and modern design trends. The conversion rate of a new site increases 2-5 times. As a result, for the same advertising$ 200 thanks to the new site, you get several times more customers from the Internet than before.