Biopace was originally designed for the tourist and recreational rider. As suggested, the primary intent was to smooth out the pedal stroke for such cyclists, increasing their efficiency. It also produces less stress on the knees of such cyclists by producing a more distinct difference between the extensor and flexor phases as the top and bottom of the stroke. Biopace does exactly what it was intended to do, when used as intended. It's intent is not the necessarily the same as other non-round chainrings, so rotating them will give a different effect. It all depends what you want out of your chainrings.

Biopace was also produced in varying degrees of non-circularity (it wasn't actually an ellipse) depending on the application. Generally, smaller chainrings had a greater Biopace effect. The Biopace effect was also reduced on higher level components, where it was assumed that owners had learned a smooth pedal stoke and there was more individuality. For instance, Biopace was never a Dura-Ace option and it was relatively mild on the 600 series. This may be one reason for the varying reported "effects" of Biopace.