As Papertiger mentioned above, it depends on the formula. There are ones to help extend wear, mattify, refresh or to give a dewy finish.
I tried all types except mattifying since I prefer satin to dewy finishes. For me refreshing spray can be replaced with any face mist or toner in a spray bottle. It's useful when you want to fix your make up. The dewy is finish is good if you have dry skin, during winter times or when you accidently over powdered your face. They both have their uses, but I find neither the refreshing nor the dewy finish setting sprays help with prolonging the makeup. It's more like a finishing spray.
For extended wear, I also use the Urban Decay All Nighter. It goes on sale often and it's not so sticky like other ones I've tried. I usually wear it when I'm out all day or if it's going to be humid. It's not magic, but I do think it helps.