What is the real difference between editing the the clip gain line and the volume line in protools 10
The difference between clip gain and volume automation is basically INPUT volume and OUTPUT volume. Clip gain is the input volume. This data is read and taken into account before insert effects, sends, volume automation, eft. Here are two examples : if you crank up the clip gain you could potentially clip your audio. If it Wasn't clipping while you were recording, it might be now that u cranked the clip gain. You don't have this effect with volume Automation because volume automation is post Fader.
The 2nd example is : say You have a compressor on a track, and you have all the settings where you want them. 3 to 1 ratio and you're getting 2 DB of again reduction. If you raise the clip gain you are raising the input to that compressor. This means that it might throw off your settings. For example you may now be getting four or five Db of compression. However if you adjust your volume automation or volume, you are adjusting the volume after the compressor. Therefore you do not mess with how the compressor is working.
Clip gain affects only that clip. The volume automation affects the actual track in the sections you change. They are both similar means to a similar end, but I've been finding if I have a track with many clips, clip gain ends up being a faster way to adjust volumes. If you need different volumes for two or more sections of the same clip, separate the clip, do a crossfade and adjust the clip gains.