You aren't missing much. The Fade effect is just another of the simple effects in Photoshop that people using Elements really think they need to upgrade for. Fade is actually provided in Photoshop as a stand-alone function. It isn't hard to replicate, as you see by examining the steps. The one thing the fade in
PS FAILS to do is that it will not fade your last step...In my humble opinion, it is implemented incorrectly as it should fade EVERYTHING, just like this easy tool allows.
Nearly every advanced tool that Photoshop has is just a more complicated application of simple tools. What I provide with Hidden Power is the mechanism to use those more complicated behaviors. Not all of them are a fireworks show. One of the most popular tools in this latest set is, however, fade...no matter how simple.
What is it good for? Some people like to use it for such things as soft-focus effects.
As a tool, it saves a few steps and makes blend manipulations possible. for example, say you apply a general gaussian blur and realize you'd rather just blur the color. Click Fade, change the mode to color, and you are done. This is instead of Undo, Duplicate, change mode, blur.
Every tool will not afford an advantage to the way you work.