By compression they mean dynamic range compression, which loudens softer sounds so they are more audible.
Pop songs for example, are heavily compressed because "compressed" music sounds "better" on cheap external speakers with bad dynamic range. Kinda like increasing the saturation on a cheap TFT panel.
And users clearly appreciate it. I was going over some bolt types with a design guy at my workplace yesterday for a project and his first instinct is to pull up the McMaster-Carr site to see what was possible. I don't know if we even order from them, since we pass through purchasing folks, but the site is just brilliantly simple and elegant.
Someone did an analysis of that site on tiktok or YouTube. It's using some tricks to speed things up, like preloading the html for the next page on hover and then replacing the shell of the page on click. So pre-rendering and prefetching. Pretty simple to do and effective apparently.