Inner-chest tension you can actually feel.
Crush the dumbbells together for the entire rep. The squeeze is what hits the chest.
Crushing the dumbbells together while you press keeps the chest fibres that pull your arms across your body under tension for the entire rep, including the top portion where a normal press goes slack. The triceps assist through lockout, but the inward drive keeps the pecs carrying the majority of the load from bottom to top. It is a smart fix for lifters who press plenty yet feel it all in their shoulders and arms.
Because half your effort goes into the inward crush rather than moving the weight up. Trading load for tension is the entire point, so leave your ego with your normal pressing numbers.
They help because the flat sides sit flush against each other. Round dumbbells still work, they just roll a little, so squeeze harder and go lighter.
They do different jobs. Flyes load the pecs in the stretch, the squeeze press loads the pressed-together position, and there is no separate inner chest muscle, just a function this move biases hard.
