Even though you can't play more than ten notes yourself (unless you've got an odd number of fingers), sustained notes eat into your polyphony, even after the key is released. Also important when multi tracking. In digital pianos, the polyphony of the piano voice may be specified as xxx/xxxstereo. This means that you may have a polyphony of 128 in mono mode, where the samples are simply panned from left to right as you go up the keyboard. In stereo mode, you have a separate sample for left and right for each note, usually cutting polyphony in half (i.e 64 in this case) but making the sound more realistic.