Volume automation vs Clip Gain Automation?

I've used volume automation a lot but never Clip Gain automation.
Can anyone explain the difference? Is it about the Gain knob vs Volume fader? Is that just to keep the fader constant so that it sounds better?

Thanks Skook
Glenn

Thanks CJ,
I just learned that the importance is that Gain (or Trim) is Pre FX whereas Volume is Post FX.
IOW any FX, such as compression, will vary what it is sensitive to if the Gain varies.
As I now understand, it still makes sense to use Gain Automation if it is mainly to make the original signal consistent in level (say fixing a section where the vocalist moved away from the mic for a bit, or a punch-in was at a different level), but not to control raising and lowering volume during the song for dynamics, say during a raising of volume from verse to chorus.