If you extrude a shape along an axis, and then you extrude that shape along a line drawn path along that same axis, it does not produce the same results.
After several hours of research and experiments, I believe these are the rules of extruding a shape along a path. { BUILD>Extrude>Path }
BASIC
1) Shape must always be in FRONT view.
2) Shape location with-respect-to (wrt) path doesn't matter.
3) Path can be in any view.
4) Length parameter for extrude doesn't matter, it will extrude the length of the path.
5) For N-Gon shapes the extrusion will be located in the center of the shape.
DETAILS
5) If you choose the shape from any other view, such as perspective, the extrusion will be as seen from the FRONT view.
SURPRISES
6) An extrusion of a spline drawn shape, extruded along a spline path, will be two or more shapes, will be different lengths and in an unknown (by me) location.
7) An extrusion of a spline shape along a straight line path will be in an unknown (by me) location.
If you extrude a shape along an axis, and then you extrude that shape along a line drawn path along that same axis, it does not produce the same results.
The above gives me enough information to have predictable results.
BTW even though the "Shape must always be in FRONT view" is a unique requirement, combined with "Shape location with-respect-to (wrt) path doesn't matter" ... greatly simplifies the usual method of extrusion alone a line. I like it.
Thank You,