Your flashmob would have been more mobile and more weatherproof with two music stands less to carry.

It extends the range of situations you can play in if you can play well by ear. Christmas carol singalongs, old people's home entertainment, whetever. Doesn't have to be in any way traditional.

Stockhausen made it a minimal requirement for anybody playing in his groups that they should be able to play back ANYTHING after only one hearing. Even if their instrument was a trumpet and the sound was recorded crowd noise. I don't imagine the Stockhausen family band did many nursing home gigs but they had what it takes.