In 2015, Google added web speed to it's algorythm (called Panda) to account for the speed of a website; especially the load speed (the time it takes for the first page to be fully rendered).
It is generally accepted that you have 3 seconds to obtain a user's attention -- or else they are gone. Yet we see many websites that take 20-30 seconds to load usig a DSL connection. Many of these websites are large commercial websites. Many others are websites developed by our peers.
To check the speed of a website, you must first clear the browser cache. On Firefox, click "History" in the Menu Bar and then "Clear Recent History". Then, using a stop watch, measure the time it takes for the first page to render. Other bowsers also have methods by which the cache can be cleared.
Browser caching was first used by the Sears / IBM / Prodigy service of the 1990's -- and it created a lot of discussion about privacy at the time. The public was ill informed as to what Sears / IBM was storing on the user's computer. Today, we allow smartphones to store many, many times more information - and do so without any discussion.