Tried them, didn't feel beneficial. Listen to your body, if you feel it, do it. If not, may want to reconsider. Personally I get a better stretch with flat flyes.
Haven't done them in a long time. However, when I used to do them I remember I prefered to do them by moving the decline bench over to the cables and using the cables to really stretch it out. I don't think it's an exercise you NEED in your arsenal, but not a bad movement to throw in every once in a while.