This is very common for a Ridiculously Human Robot who may need to eat food to maintain The Masquerade, but it's certainly not limited to that trope. Some robots consume food as a power source (Calories powering machines is something that exists in the real world, though in very early stages) either for convenience (or rarely for horror). Other robots may eat food they have no way of processing and no logical need for as pure Rule of Funny hedonism and to anthropomorphize otherwise non-human machines. Despite being unable to digest food, don't be surprised if caffeine, sugar, or alcohol still somehow affects a robot's behavior.