The main benefit of using dumbbells is that it requires you to engage a greater number of muscles compared to the barbell and machine variant and actually activates the lower fibers of the chest press better than a barbell press — since your hands are free to move across your body when you use dumbbells, the lower
pecs get a better workout.
In addition, when I use gym equipments (not necessarily lift heavy weight I'm not a big guy, I weigh 150 lbs with relatively medium bones) but dumbbells, Lat Pulldown, Hyperextension,
Pec Dec, Leg Press... etc my muscles
get really tight in short time and I feel the results as
well as it motivates me more to
workout at the gym.