This is a really cool resource to play around with Variable Fonts. Not only can you adjust the font weight and width, but you can also adjust the ascenders, descenders, x-height and other more advanced settings in some of these fonts.
To me the difference between Variable Fonts and Static Fonts is the same as picking a colour from a grid of colours versus using an RGB colour space to pick one. Eventually, brands and designers create their own colour schemes for consistency instead of playing around with the colour space all day. Similarly, I can see designers wanting to create their own typeface-schemes which specify the attributes for different requirements like Headings, Subtitles, etc.