It’s not just about the difficulty of the music. There are simple pieces for pedal harp that would not be playable on a lever harp without modification.

For example, if there is an accidental while both hands are playing and no chance to preset the lever, for example if the same note is natural on one beat and sharp the next, piece would need to be tweaked, perhaps one if them moved to a different octave or played without the accidental, to work on a lever harp.

In addition, glissandos can be very different on a pedal harp because of the ability to play both flats and sharps, and change all the strings at once. In the key of C major, a glissando from C to C on a lever harp will be CDEFGABC, a scale. On a pedal harp, this is possible, but the harpist can also use the pedals to create a different sound very easily. Setting the Bs to sharp and the Fs to flat, a common pedaling in that key, would make the pitches CDEEGACC, which sounds more like a chord and is very resonant, bright, and doesn’t get muddy when played over several octaves over and over.