There is nothing like a heavy barbell. That being said, dumbbells are a nice break, they let you work on stability more, they're good for off the chest strength, they don't beat you up too much compared to max weights on a barbell, and it's easy to not kill yourself if you don't have a spotter. In theory they also allow a greater range of motion, but most of the clowns I see using dumbbells in lieu of a barbell actually have less range of motion than they would if they touched a bar to their chest. I use dumbbells every 4th week or so on my current training regimen.