If the website contains many sophisticated-looking things like animations etc. it makes many people think you must know a lot because you can come up with such a stylish and sophisticated web-site.

In other words it serves as part of the portfolio of your technological prowess. It does not really help the user of the web-site, it helps to fool them into thinking your product must be awesome. The web-site is part of the product, it's the box around the thing you sell.