This gives a spill a lot of room to spread. With upholstered fabric, you have a thin layer of fabric to penetrate. Once the stain is in the stuffing, it is more difficult to remove. With carpet, you could even “pull the carpet up” and deal with problem spots from underneath if you had to. But not upholstered fabrics.

A good quality fabric protector will assist in resisting spillage,
and keep normal soiling such as airborne soils, dust, pet dander, and perspiration on the surface for easier removal. Keeping your upholstery protected will help you keep your upholstery looking better longer.