The Fifth Leg
Look under the front of most three seater sofas and you will find four legs, one at each corner. That is fine on a two seater and marginal on a three, because the front rail spanning between the front legs is carrying a substantial share of the seat load and is behaving as a beam. Beams deflect at their midpoint. Over years, that deflection becomes permanent, the front edge of the seat drops in the middle, and the cushions start to slope inward. It is one of the most common ways a long sofa ages badly, and it is entirely a design decision rather than bad luck.
Adding a fifth leg under the centre of the apron halves the span and removes the problem. It is not free to do. The carved apron has to be laid out so its ornament resolves around the centre leg instead of running through it, which means the scrollwork is designed for this specific arrangement rather than repeated along the rail, and the leg itself has to be carved to match the four at the corners. Most manufacturers skip it because it costs money and nobody notices its absence in a showroom. We add it because the difference shows up in year eight, not week one. The whole frame is carved and assembled by hand by master Indian artisans.