Like Nails on a Keyboard
Learning to play with a relaxed, but rounded, hand helps immensely with piano or organ technique. A rounded hand transfers energy from the shoulder all the way through the fingertips. One of the things I say most often in my intermediate and lessons is “high wrists, round fingers, please.” But this is impossible to do with long nails.
When nails are long, they click on the keyboard, unless you play with a flat hand. This works okay for slow songs or pieces that only use the larger white keys (they used to be black). But once you start dancing around the keyboard or playing the smaller taller aka black keys, a high wrist and round fingers make all the difference.
This is a concept I myself did not understand well in high school when I gave my smaller-than-Beethoven’s hands carpal tunnel while learning this).
Trimmed nails, in other words, are a preventative measure against strain and overuse of the hands and wrists.
Longer nails are popular, I know. And sometimes nails grow so fast that it seems like it’s almost always time to cut them. But take it from someone who learned the hard way: the time it takes to make fingertips available to the piano keys will pay itself back in music.