Voice of the customer is effectiveness. This is a metric that shows how well we met the customers requirement. Eg. Quality.
Voice of the business is effeciency. This metric shows if customer satisfaction was achieved profitably. Eg. Average Handling time.
In my current company some trainings went digital in 2017, which is efficient ie no trainer or training rooms are required, but NPS and CSAT dropped considerably as compared to 2016. Training became efficient but less effective.
My previous medical transcription company had 2 layers of processing -Transcription and Editing. Due to quality issues we added another layer called Superediting which improved quality ie it was effective to satisfy customer, but added cost to the business. We became more effective but less efficient.