It can happen. In the midst of multitasking to the point where your desktop is awash in open windows, you can lose sight of your cursor. Instead of mousing about frantically or calling up the right-click menu momentarily to find it, El Capitan has a better way.
And it is this:
Simply wiggle your your finger on your trackpad and your cursor will grow to an implausibly large size to aid your search efforts. Stop wiggling and your cursor quickly shrinks to its usual size, with its coordinates now known.
For more, get all you need to know about OS X El Capitan.