Bigger stretch, fuller chest than the bar.
Keep your shoulder blades pinned back and wrists stacked over your elbows.
With a dumbbell in each hand, your chest gets a deeper stretch at the bottom and a squeeze at the top that a fixed bar can't offer, since the weights travel in and together as you press. Each side has to control its own load, so a lagging arm can't hide behind a stronger one. The triceps assist through the top half of the press, but the longer arc keeps the pecs doing the bulk of the work.
Better for chest stretch, freer shoulder paths and fixing side-to-side gaps. The barbell is better for absolute load. Most good programmes run both rather than picking a winner.
Rest them on your knees sitting on the bench, then kick one knee up at a time as you lie back so the weights arrive at your chest. Never let them hang behind you at arm's length while you wriggle into place.
To chest level or slightly below, wherever you feel a strong pec stretch without the shoulders complaining. The extra depth is the whole advantage over a bar, so don't cut it short.
