Yes, it would be useful to (be able to) hide them - if as per proposal you can only do so when they are in the default position.
The proposal mentions locking. Possibly more useful is 'discretising'. E.g an option could mean the pan slider could be allowed to only exist in left, middle or right state - or allow five states for each slider. With five states it's still going to be obvious if the slider is out of position. I am also tempted to make the slider pip larger if it is exactly in the centre position as a visual cue. It might make people think 'zero position' with the circular slider pip design. A themer could make the larger version a different colour too, but I probably wouldn't on my themes.
When in five-state mode the slider line could change to indicate the 'stops'.
If we do have (the option of) five stops, we don't need to have the option of hiding the sliders, but the option of locking could still exist. To avoid the stuck-in-a-mode problem, a locked slider could still be moved if you click and drag it far enough - because then it is not an accidental drag.