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Where can I start?

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Owl:
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,

ENSONIQ5:
When extruding along a path, you MUST consider the mathematical origin of the shape, which by default will always be located at the centre of the bold grid crosshairs bisecting your workspace.  This is the point that will be traced along the path, so if this point is not centred within the shape and is in fact nowhere near the shape (eg. if you have created your shape in the top left of your workspace) the final extrusion may not end up where you intended (but always predictably, the offset will be based on the location of your shape's origin point relative to the shape itself).  The generated mesh may also not look like you would expect, in fact if the offset is significant and the path quite convoluted the resulting mesh can look nothing like you intended.

This is not an issue with axis extrusion since there is no path location to be accounted for, the extrusion can just extend into the chosen axis dimension... hence the difference you have encountered.  Always create your shape to be path-extruded around the centre crosshairs, if this is difficult due to other meshes on the screen just create a new Object to work in (I usually create an Object called "Workbench" in which to build things, cutting and pasting into the main Object as required or into other Objects that will be added as Elements in a Scene).

NOTE:  In the above I have capitalised Objects, meaning 'work spaces' created in Object mode, to distinguish them from meshes such as extrusions, lathes etc.

Owl:
We must be talking about two different things.
Try putting a Bunch on N-Gons all around the FRONT VIEW.
Put in one spline path, then extrude each of the shapes down the same path. They all extrude in the same place independent of where the shape is, they all extrude down the path.

ENSONIQ5:
I am talking specifically about shapes you create with splines.  N-Gons have their origin point located at the N-gon's centre, so yes, they all map directly to the path and all is well.  If you try it with a random shape created from lines however you will see what I mean.  Where the mesh ends up is also dependent on the view within which you created the extrusion path.  Try creating two paths, one in Top view and another in Left view, and map the same shape to both.  You will notice that the meshes rotate differently since each path has a different X,Y,Z frame of reference.  I should add that this is with the coordinate system set to screen coords, I have not experimented with changing this to see if it has an effect on path extrusions (but will do so *).

There will still be a difference between axis-extrusion and path-extrusion for N-gons however, since the latter will still map the N-gon's origin to the path, so the mesh won't be in the same place as if it was axis-extruded.

EDIT: * Nah, not a good idea.  Changing the coordinate structure forces spline creation to adhere to the left/middle/right mouse button thing (each relating to a difference axis) so not practical for drawing paths.

Owl:
Is there any documentation or tutorials on: Object/Axis ^O   

Also, I can't find the three coordinate systems choices ever doing anything. They seem like a necessary tool.
I'd like to move and move about the selection points.
Thank You.

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