In spite of the availability of tens of thousands of hand-knotted rugs, designers and their clients sometimes require a custom designed rug. The reasons are varied.
Polyurethane is a protective coating that covers and seals the wooden floor underneath. It imparts a shiny, gymnasium-like floor. It can and does look great.
Although the area of the floor is relative small compared with the walls and the ceiling, it's a room's most important surface.