Thanks brother. It feels good to have the time to devote back to the community in this board and others.
Shoulders are the most mobile and the least stable of all joints. IMO what IG means is you will see a lot of guys doing fly work and over exaggerating the open aspect of the fly. It's overkill for actual work done to the pectoral muscle and can injure the capsulitis tissue of the shoulder.
Slow and concentrated movements during fly work will build the pecs more than most realize. The negative movement during a fly is just an important building block as the positive movement. I used to go heavy with flys... No mas!! 35's or 40's 12-15 reps. Slow contracted movements and squeezing through the whole movement.
I know everyone is completely different and reacts to exercises differently. When I changed from lifting for power and strength and moved more towards slow controlled contracting movements my body started to shape differently and much more rapidly.
I spend far less time lifting now. My joints feel better and I don't ache near as bad. I still get nice and sore but not that sick achy feeling.
Kinda going with the mindset, "I want to build my body, not lift a bunch of weight."