Different paint sheens behave differently. Matt hides imperfections but can be harder to clean. Satin and semi-gloss are easier to wipe but show bumps and patches more. Using them smartly in one room gives you the best of both.
For example, walls in a matt or low-sheen finish look soft and even, while doors, trims and skirting in a slightly glossier finish stand out and are easier to clean from scuffs and fingerprints. In kitchens and bathrooms, you might use a more washable sheen on areas that are likely to get splashed.
Visually, the subtle contrast between matt walls and slightly shiny woodwork adds depth and detail. The room feels more layered and “designed” without using different colours everywhere.
It’s a practical trick disguised as a style choice.