One of the most common uses of variable fonts is to make animations. You probably have already seen it: fonts that gain and lose weight, get wider and narrower, or even morph between a normal font and a stencil version, always incredibly smoothly.
You don’t need to buy expensive software to do that. In fact, a lot of these images are made in Drawbot, a free application for MacOS. Although Drawbot was initially developed as a tool for learning to code in Python, the fact that it can export in PDF, SVG, PNG, MP4, GIF and other formats made it an excellent tool for automating tasks in graphic design. You can even typeset a whole book in it and then export it as a print-ready PDF with CMYK colors!