As I understand it, notify was (is?) required so that Hijack can see when the player application has started enough to be able to send it a signal to ``restore visuals''. It does this by watching the notify data that the application spits out of the serial port. However, the default speed of the serial port in the car is 9600 bps, not the 115200 bps that it is on AC power, and that's slow. Sometimes slow enough to mess things up. Making the speed faster (or preventing that data from actually travelling out of the serial port, via suppress_notify) prevents that from happening.

Note that this is all conjecture on my part, but I'm pretty sure that it's at least close to the truth.