Well personally, I could see the advantages of androids over humans. Especially if, say, they're used as soldiers, hunters, or mercenaries. Rather, than just workers. You could mass produce them, rather than hiring them, or in the case of slaves, capturing or breeding them. Robotics could provide increased strength, speed, processing capabilities, higher accuracy, etc. Presumably, they wouldn't be as susceptible to fear or stress. So there are definitely a number of advantages to androids over humans for this work.