Smartphones typically have a restricted output current for OTG devices. Furthermore, there is a lot of interference inside the smartphone, so powering from a smartphone 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 dongle receives superior quality power with minimal interference with the CB19 while simultaneously not draining your smartphone's battery, and you obtain optimal performance from both your phone and the dongle.