Their own product page mentions "zooming in/out, adjusting screen brightness, brush size, volume, selecting video clips or photos, or backlight hue". Someone here mentioned adjusting parameters in audio software. I can add that it can also serve as a replacement for the mouse wheel in some cases. Another cool use is controlling the knobs in the MCP panels (i.e. the autopilot controls) of aircraft in flight simulators, if you don't already have better hardware.

But really, in general, anything that would require pressing the same key a variable number of times in a row might benefit from a knob control, especially if it makes sense to do the same thing in some "opposite" direction. And especially if you do that multiple times per day. So it kind of depends on how you use your computer.

You could use it to scrub through videos, scroll pages, zoom in or out, scroll through undo/redo history, etc.