Flys are a chest exercise that you can do. View it here for a better view of what it is. As you can tell it works the best, but it works it in such an indirect way that I really question the amount of benefit you can get out of it.

I’ve been doing these for sometime now and from what I’ve experienced, they’re a waste of time. They don’t provide you with any muscle gains or results. They don’t help you get over plateaus, they’re just a big waste of time. I see a lot of people doing them at the gym, and I guess that comes down to the whole idea that ignorance rules at the gym.

I suggest that you stick with bench presses because that is going to give you the best workout on the chest. I don’t really see the point of doing flys, but if you feel the need to do it - do it at the end of your workout, so you don’t waste any good energy on the exercise.