WordPress is a large platform, and there are a variety of truly massive databases and websites that get queried constantly. It increases the bandwidth usage and slows down websites. Any customer of web hosting knows that bandwidth is an expensive thing especially when you need to upgrade to a premium plan because of a lots of queries. You may consider it being a part of your website growth, but that is not really true.
In order to prevent the slowdown of a website loading times, there are a number of helpful and innovative plugins that actually cache database queries and websites.