Very new to the double bass, but I wanted to ask why is it so important to lubricate the groves in the bridge before changing string, and how this affects the playing?
It is my understanding that lubricating the grooves on the bridge helps them slide smoothly. Without it, there is a strong possibility that the strings will pull the bridge towards the fingerboard. This can potentially cause the bridge to warp over time, not be seated against the top properly, or even collapse (fall over).
I am not aware of any playability issues. Graphite has been used for as long as I remember on the string grooves.