How I have used the expression pedal.
1-No rhythm--As you listen to an orchestra playing waltz, semi classical selection, or a solo instrument---they do not play at a constant volume. The changes in volume do go beyound that of the touch sensitivity of the keys on the keyboard. Sometimes down to a whisper, returning moments latter.
2-I use it for my solo part, Rt1, Rt2. When the pedal is at ful volume, I am playing a solo. When I am singing, that same sound is lowered, putting it in the backround. No buttons to press. Nice.
3-I also use it for my left hand sounds. It's nice to hear a backround sound vari, it adds alot.

On that note I will say, I never take the pedal to a job, it is another thing to worry about. There is enough going on without adding more stuff. The one time I did use it, I couldn't remember if I was full volume or half, or whatever. It is a good feature, I imagine with a lot of patients it would bring a player to another level of playinmg.
In my humble opinion, John C.