The parameter is intended to shift the footing over, from interior to the exterior face of the wall. The footing starts out centered on the wall above.
The maximum eccentricity is equal to (Footing Width/2)-(Wall Thickness/2).
The interior wall surface can be aligned (flush) with the interior face of the footing but not further, creating any overhang of the wall, which seems logical to me. A picture might help?