The only link I clicked on is the link to the MIDI concertina. I don't know why the owner modified it, but here are some possibilities.

Suppose he has sounded out a dance tune, which he plays with muscle memory. (If he's done one, he's probably done many.) Now that the concertina is connected to the computer, he can use music software and tell it to 'listen' to his playing. If he plays carefully, he will get a good MIDI file of a tune.

The same is true of a tune he composes himself.

Once he has the MIDI file, he can change the key to suit a different instrument. He can put it in bass clef to suit a cellist. He can put it in alto clef to suit a violist. He can put chords on it easily when he can see the dots and sticks. He can e-mail it to friends so they can hear it. If any friends have music software, they can get it as a MIDI file and do all the same things.

And sure, the sound of the concertina may not be all it should be. That's not the point. The point is to get the power to be creative and to have a good time.