Page speed can be described as the “Loading time of a webpage” - how long your browser takes to respond to the webserver and loads the complete content of the webpage.
For SEO - No matter how you measure it, a faster page speed is better. Many people have found that faster pages both rank and convert better. Also, Google gives hints that a faster page will rank higher.
Secondly, if we think about UX then you always want your page speed should be high. A slow page will tend to have a high bounce rate as users don’t want to wait for the times. Similar is the case with mobile browsers, your page should load faster on mobile devices.