balanced systems were developed by pro audio because they are much more manageable from the S/N point of view, where in pro setups. frequent connecting and disconnecting are the norm, and often with long cable runs. They don't want to faf around with hum problems while a band is waiting to record for example.

There are true balanced systems and also other variations which approximate to balanced. ATC active speakers for example have balanced I/Ps. As has been said, the circuits have twice the elements in them, and usually about twice the distortion, bt in reality it is probably still insignificant.

I am happy with balanced pre and speakers, but FM O/P has an unbalanced O/P, and also my CD player, but it is very much more usual to feed a balanced I/P from an unbalanced O/P, than the other way round.