Most of the dust in a room ends up under things: sofas, beds, sideboards. A straight wand means getting down on your knees or moving the furniture.
It bends, you don't
A folding wand bends in the middle so the floor head stays flat under the furniture while you stay standing.
Reach the back wall
Fold it flat and push it right under the bed. The LED headlights show you what's under there.
Easier to store
Folded, it takes up less room in a cupboard or a corner.