This is one of my favorite changes on the E9th.
Almost every PSG has it and it really opens up the potential for interesting voicings and outside chords.
The basic use is as a Major, second inversion chord 3 frets above the open position with the A pedal. But if we engage the F knee lever without adding the A pedal, we have a dominant chord or a diminished chord, depending on context. The end result is a dissonant sounding triad that seeks resolution and an easy to grab voicing that can fit in many contexts. I’ve composed a Blues in the key of C that illustrates the point.
Just a note, the ending chord is a C9 in the two below position with the A pedal. other than that, everything is with the F lever.