Like Dakotaraptor and Microraptor, most dromaeosaurids had fearsomely sharp serrated teeth, flappable wings, and sickle-shaped claws. The recurved claws were used for latching onto prey, preventing their escape. Claw size was relative to prey size.
This strategy is only really needed for prey that are about the same size as the predator: large enough that they might struggle and escape from the feet. Smaller prey are just squeezed to death, but with large prey all the predator can do is hold on and stop it from escaping, then basically just eat it alive. ~ English paleontologist Denver Fowler
It is a modest modification to go from a claw for snagging prey to one for perching: a prehensile pre-adaptation. (A pre-adaptation is a trait that evolved for one purpose which then transforms to another function.)
Flightless, feathered wings were also a pre-adaptation: originally for flapping to stabilize oneself while holding onto struggling meals-to-be. To take flight from there was not such a lofty advance.
Many structures in modern animals originally evolved for quite different purposes. ~ Denver Fowler