SustainPedal padding?

[Phil Holmes]

I'm currently working my way through the regression tests trying to find 
features only documented there, and have arrived at pedal-ped.ly.  I've 
worked out how the pedalSustainStrings uses the pedal glyphs, but can't see 
that the following line:

 \override Staff.SustainPedal #'padding = #-2

has any effect at all.  I can guess what it's trying to do, but doesn't seem 
to do anything.  Anyone any thoughts?

--
Phil Holmes