Smartphones typically have a restricted output current for OTG devices. Furthermore, smartphones yield a lot of internal interference, so powering from them isn’t the most ideal.
With the CB19, dongles can power from a clean source, such as a power bank, instead of your smartphone. Your DAC dongle gets quality power with minimal interference with the CB19 while simultaneously preserving the battery on your smartphone, achieving optimal performance from both your phone and the dongle.