SVG: when to use animVal / baseVal

When does animVal and baseVal of an SVG element differs. When is the appropriate time to use them to get the correct value. The verbatim difference can be read based on here, but I am more concerned when all these values can differ. Any transformation, or scaling affects it?

Form another post at SO here

function rectCorner(rect){
pt.x = rect.x.animVal.value + rect.width.animVal.value;
pt.y = rect.y.animVal.value + rect.height.animVal.value;
return pt.matrixTransform(rect.getTransformToElement(svg));
}

what is the rationale using animVal here?

thanks, bsr.