Setting powder reduces shine
A translucent or skin-matching powder goes over foundation and concealer to reduce shine and absorb excess oil, especially on the forehead, nose and chin.
Setting spray melds the layers
Spray is used as the final step after all your makeup. It helps the different layers blend together for a more cohesive look and extends overall wear.
Oily skin may need both
Oily skin often benefits from using both: powder to absorb oil right after makeup, and spray at the end to lock all the layers in place.
Beware of too much powder
A lot of powder in one place can look dry or cakey instead of natural. A thin layer with a brush or small sponge is usually enough.
Choose a spray that suits your skin
Some sprays have hydrating properties that suit dry skin, while others are mattifying and better for oily skin.