Variable font technology is an innovation that allows you to adjust the size, weight and style of the fonts. These individual font files actually behave like multiple fonts, allowing you to adjust the weight, width and slant of type as you work.
Standard fonts are separate files for each style, weight and type. Font files are relatively large and when there are a lot of them, it becomes a performance issue. This leads to slower load times and latency.
Some benefits of using variable fonts
Less font files translate to faster page-load times. This is arguably the biggest benefit of variable fonts on the web.
Standard fonts of many files can be compressed into one variable font file. This means that browsers will have less files to download and so, less loading time.
Fewer compromises for designers
Designers who are conscious of file size do not need to compromise their design. The use of variable fonts eliminates the need for trade offs for the benefit of speed.
Variable fonts allow users of the font to adjust the fonts to suit their aesthetic or visual needs.
A user who has problems viewing small fonts can adjust the fonts to a more readable size.
Tons of style combinations
A single variable font can support a large number of styles and variations. Unlike standard fonts, there is no need for a ridiculous number of files that will slow the browser and reduce customer satisfaction.
Text animations and transitions
Because the font style, weight and all other parameters can be modified, font can be used for animations and transitions.
This eliminates the need to for extra css libraries which may further slowdown the browser.