Initiating each rep from the bottom of the movement puts extra focus on the "isometric" portion. This can have huge carryover for your strength, hypertrophy, and even your shoulder health and stability.
Focused isometrics have also been shown to lead to greater muscle activation than their concentric and eccentric counterparts. They've also been shown to create an occlusion effect in the muscle. This means blood to the muscle is increased while blood flow out is restricted, so you'll get a pretty nasty pump going.
Feel free to play around with angle of the bench on these, but a low incline works best. It's easy on the shoulders and it hits that upper chest just right.