Better shaping of the stays'l for when on a beat, heavy halyard tension and loosened outhaul ... it ''rounds" the luff entry section of the sail for better aerodynamics when flown 'under' a topsail/genoa. The stay wont be seen as 'drawing' but it vastly reduces turbulence at the mast for better mainsail performance; hence better genoa performance.

Loose foot works FINE, easier to control the shape.