My usage:
I use it to stop my Mac from going into screensaver mode with every few minutes of inactivity, per corporate IT mandated settings that I can't change.
Mode 1: (This is the mode you get immediately after long-pressing the button that powers on the device)
Oftentimes I like to read part of a document on screen and think about it at length, which easily causes a few minutes of inactivity, but on occasion I might want to use the pointer to interact with, say, the browser. So I use mode 1, which causes the mouse pointer to move imperceptibly from side-to-side, so that it doesn't interfere with my using the pointer when I choose to do so. The other two modes (2 and 3) move the pointer way too much to be able to manually control the pointer, but I understand they are meant for a different purpose that does not require occasional manual control of the pointer.
Caveat:
If you're using mode 1 on a Mac this can magnify the pointer all the time if you have the accessibility feature "Shake mouse pointer to locate" on. I don't see this as a deal breaker since it's always possible to turn the accessibility feature off but it's probably still worth knowing that a simple workaround is needed before you buy this.