I guess it's partly tradition, the non-rotating type of "sweep" has been grouped under extrude in NURBS modelers before.

It fits somewhat because without any rotation you are much more limited in the path shape that you can use, you kind of have to use one that goes fairly straight, you can't make a good surface with a circle path for instance, because the shape will fold over on itself.

So in that sense it is kind of like a guided extrude, since simple extrude is straight.

Also calculation-wise it is quite different from sweep - there are some special properties to the extrude with set path. It preserves the control point structure of the path curve in the resulting surface, while sweep goes through a fitting process which is a little different.

So another use for Extrude with Set Path is if you want a straight extrusion, but with say 4 control points along it - you can draw a curve in a straight line using 4 points and use that as your path and get an extrusion with 4 points in it. People have requested being able to set the number of points along the extrusion, and set path allows for that, so that is another reason it is under there...

- Michael