When I see eagles, they're usually eating road killed deer. I actually saw one the day I made this thread. It was flying above the hawk. Probably waiting til the hawk caught something so it could steal its food...
Would you not do the same in the wild? All that active hunting is stressful, let someone else do the work and use your bravado and might to steal it like the dominant beast you are.
But yes, eagles will do this. They will also hunt on their own. It partly depends on the quantity and quality of prey in their nesting grounds. Around here, there is plenty. That's why waterways are their primary nesting/hunting grounds, because there tends to be more prey available; they can either swoop in and snag a fish, or chase after any of the numerous critters that tend to congregate near water. It's a breeding ground for bugs, which draws larger insects and smaller predators that love those insects, and small mammals who like all of the above. It's fertile land, ripe for Bald Eagles.
But they are intelligent, and opportunistic. There's a commonality with intelligence - opportunism. Crows are highly intelligent, but tend to be a scourge, because they take advantage of a situation.