By mounting the engine forward of the wing you to some extent minimize the aerodynamic interference between wing and nacelle (engine) - since the thickest fart of the wing ends up behind the thickest part of the engine.
More importantly, by hanging mass off the front of the wing the aeroelastic characterists of a thin wing are improved, which means that less additional structure is required to stiffen the wing, so there is an element of weight saving, even accounting for the additional structure to suspend the engine forward of the leading edge.
(Some older aircraft have 'flutter bodies' on wings or tail surfaces - ballast weight forward of the leading edge in faired bodies - in lieu of engines hung forward.)