ERC is when a morph (or joint)is set by another channel.
A "channel" can be anything in the second section of the CR2 which is called 'channels', strangely enough.
These are morphs or joint movements mostly. Scale is a channel. Any thing that you can change the dial for, can automaticall change the dial of another, either on the same figure, or a different one. When this happens on a different one, and you do not want it to happen, it is called cross-talk. Poser 4 is sort of at v0.5 on this feature, so it is tricky to use in practice, you must CYA.

Relevant to this, suppose you had a morph for the 'hip' part of the skirt that goes to the hem. At 1.0 this morph swings the section up 90 degrees so that it fits in with the part covering the legs.
You can do the morph by hand, after you do the sitting pose. Or, you can slave the morph to the bend rotation channels (P4 thigh only) of the figure. This is a tricky example, but say 90 degrees of rThigh = 0.5 morph and the same for lThigh. So, if both legs have 90 degree bend, the morph is at 1.0. It is set automatically by bending the thighs of the figure. Enhanced Remote Control.
You set how far the morph can go with its own min/max.
You set how fast with the rate (DeltaAddDelta) on the morph itself. How this morph looks with different positions for the legs would need testing, but I think this would probably work for most poses. One morph, it does not save a lot of time, but suppose you have twenty different morphs to adjust the skirt to different poses? Or suppose you were doing an animation?

An example of ERC that is in more constant use: slave the xrot and yrot of the left eye to that of the right eye. When you move the right eye 10 degrees to the outside, left eye automatically moves in parallel. This is JCJ - joint controlled joint. The rate is 1.0.