It is impossible to guess how many days have been saved by flies like an any, beetle or grasshopper (terrestrials). My earliest experiences were with a grasshopper given to me by another fly fisherman I met on a windy day on the Madison in Montana. 

This article does a very good job of describing the techniques I have learned over many years. With a couple of "hoppers" in your box and these tips, you will be ready the next time the winds threatens to blow you off the water...click here for more