When should I open an under-stairs nook for storage access?

Open an under-stairs nook for storage access when the space is deep and hard to reach from the stair side, making normal use impractical. Creating a hidden door from an adjacent room lets you turn the nook into a tidy seasonal closet without obstructing stair light or flow. This smart door solution keeps the stair-facing side open and visually calm while adding functional storage behind the scenes.