Flies are useless

the fly reduces the use of the stabilizer muscle that are more engaged in a pressing motion such as the triceps. Another advantage of the the fly is the ability to stretch and work the pecs using a lighter weight than a press ( if you are limited at home with a lack of weight the fly has a great advantage to your chest routine over a press )
The dumbbell fly also eliminates the elbow joint in the movement.  

I never said flies dont stretch / work the chest. But the fact is the pec major is not worked anymore whether in a fly or press position.

Flies are not useless.
It's a good exercise for isolating the chest. IMO, they should not be done if you are not advanced. It's proven that changing the exercises you have never done before increases the size of the muscle or strength. Here is the website.
http://www.exrx.net/WeightTraining/ChangeWtEx.html
According to t-nation it does work your chest well, even more than pressing movements.
Here is a table, you can check this out
http://www.t-nation.com/free_online_article/sports_body_training_performance/inside_the_muscles_best_chest_and_triceps_exercises
I don't agree with you that flies are useless. It's a good exercise  

I already explaind to you it's not the same and again as I mentioned when you get higher in the weights its DANGEROUS!!.. I'm sorry but im not going to be twisting 110lbs dumbells when I can do flies which is far superior to just twisting dumbells

@kaplanT4,  Did you look up the muscle mentioned in the Vid or not ?? the guy is giving his opinion and not providing evidence to back it to get business.
You only have to feel the pec with one hand to feel the difference, look at Arnies fly from the bench to floor, there is no way a press can stimulate the outer fibers as his rediculous ROM, Look at Gironda`s hybrid between press and fly, far more stimulation than a standard press. If you got 2 years experience like you say, How have you proved this for yourself?  The stupid mistake most take is not understanding the muscles used in a compound and don`t know how to drop the weight for isolation exercises like this where triceps are not a major player. This lack of knowledge  is prob the main reason beginners are encouraged to stick with simple compounds but it is exploited by many trainers..

Agree with the guy in the video but there is 2 more points which should be considered. The first is moment arm length and how it makes these exercises differ. Moment arm in flyes compared to press is roughly doubled making it a lot easier to work the chest with a lot lighter weights to get the same stress to your chest thus it might be easier on the shoulder joint if done properly. = It's harder to come out from the hardest position of the lift. The second part is that fly is an isolation exercise without forearm extension = Pectoral muscles + deltoid will generate that torque which brings the weight up. Making it good for person who lacks weights and his dumbbells got light for pressing or who wants to work his chest and delts without working triceps.

Mighty paint skills to explain my point:


Agreed with Paralysisxiii

Awesome paint skills!

Flies feel good... Isolation isn't bad at all, they are great for that finishing touch.

Well done I tend to agree with you two, and love ring flies. However, what you said about them being easier on the shoulder joint does not follow. You use lighter weights, because of the longer levers, but the torque will still be important (because of the long levers!), and it isn't distributed over several joints. For that reason, they can like other isolations, be really tough on the joints too