Toners are designed to be used after cleansing your face and before your serum and moisturiser. Think of your freshly cleansed skin as a dry sponge. You can put a thick layer of detergent on that sponge and it will sink in a little, but mostly just sit on the surface. Now imagine lightly wetting the sponge, the detergent is going to skin in much more deeply and spread more evenly. 

Unlike toners, you can apply a mist whenever you like. They are great to keep on your desk or take on a plane for a quick skin refresh. You can spray your face before applying make-up for a smoother and more hydrated skin, or use throughout your skincare routine to lock in moisture. They work nicely in between cleanser and serum, or even before and after moisturiser for a deeper penetration of your product.