Chest training often defaults to a single flat-bench movement repeated indefinitely — a genuinely well-rounded session covers more of the muscle than one angle can.
Angle variation targets different fibers
Incline, flat, and decline pressing movements each emphasize a slightly different part of the chest — rotating through them over a training block builds more complete development.
Isolation work has a place, but not first
Compound pressing movements should come before isolation work like flyes in a session, since they demand more energy and coordination while a member is freshest.