Robert Estrin on LivingPianos.com provides two main reasons to change fingers on repeated notes when playing the piano.
For Rapid Repeated Notes: Fast, repeated notes are almost impossible to play with one finger. Different fingers can enable a faster pace.
To Achieve True Legato: Changing fingers on repeated notes can lead to a smoother sound. The motion of lifting a previously played finger while the next one is coming down facilitates a more seamless transition between repeated notes, enhancing the legato effect. This technique proves effective even without using the pedal.
Despite these points, the same finger can be used on repeated notes in instances that do not require extreme legato or are not played at a fast tempo, and can still yield satisfactory results.
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