Is a cummerbund there just in case your flies burst open ?
Have you been watching The Sewing Bee? I think they explained that a cummerbund gives a stream-lined join between shirt and trousers. Note that consumption of too many Cumberland sausages would affect your silhouette.
editted to add:
Aesthetic and Historical Significance
Originating in
colonial India, British military officers adopted the local
kamarband (waist sash) as a practical solution for hot climates, which later became a fashionable accessory in Western formal dress
Wikipedia+2. The cummerbund’s pleats traditionally face upward, historically used to hold small items like opera tickets or coins, though today this is largely symbolic
explainthat.org+1. It is typically made of
black silk or satin to match the jacket lapels and is worn at the
natural waist, covering half the shirt and half the trousers
explainthat.org+1.
