Most Borg drones were portrayed by actors wearing elaborate costumes and heavy makeup. Even drones that just stood still were often played by actors, since they looked more realistic. But in some cases, drones seen regenerating in the background or on upper levels of large sets were represented by these dummies. They had the distinct advantage that they didn't mind spending all day standing motionless in a precarious alcove, nor did they ever need to get out of their Borg suits to go to the bathroom!