Well, making the cost artificially high can be a point in itself. Sometimes the concern about a technology is the ubiquity and scaling.
But aside from that, to address your questions:
1. If there's a human in the loop, the human can be accountable. Explainability and accountability of algorithmic decision-making is an emerging concern, especially to the extent that algorithms may encode bias in their training data.
2. Real-time systems. Being real-time qualitatively changes the impact this can have on your day-to-day life. Taking the human out of the loop makes many applications feasible that otherwise wouldn't be. Like doors.
But aside from that, to address your questions:
1. If there's a human in the loop, the human can be accountable. Explainability and accountability of algorithmic decision-making is an emerging concern, especially to the extent that algorithms may encode bias in their training data.
2. Real-time systems. Being real-time qualitatively changes the impact this can have on your day-to-day life. Taking the human out of the loop makes many applications feasible that otherwise wouldn't be. Like doors.