Piercing a Rail That Has to Carry Weight
Cutting openwork into the crest of a sofa back is decorative and reasonably safe, because nothing structural passes through it. Cutting openwork into the apron below the seat is a different proposition entirely. That rail ties the front legs together and resists the frame spreading under load, and every void removed from it takes away material that was doing a job. It can only be done if the member is deep enough to keep a continuous solid path around the piercing, and if the timber is strong and fine-grained enough to hold the remaining sections. Most makers simply carve the apron in relief and leave it solid, which is easier and shows less.
The reason to take the harder route is what it does to the sofa's weight in a room. A large carved sofa with a solid apron sits on the floor like a block. Pierce it and light passes under the seat, so the piece appears to stand on its legs rather than to rest on the ground, and a substantial three seater loses a great deal of visual bulk without losing any of its ornament. Combined with the pierced crest above, the whole sofa reads as a frame with fabric in it rather than as a mass of upholstery. It is cut, gilded and upholstered by hand by master Indian artisans.