A lot of people wonder about the use of feeder fish for their larger carnivorous friends. Opinions on their use is mixed, but I feel that the occasional feeder guppy provides a chance for your fish to exhibit natural hunting behavior and relieves him of boredom. However, some people argue that the use of feeders is cruel since the guppies or goldfish do not have a chance to escape as they would in the wild. Additionally, continued use of cheap feeders like goldfish are actually bad for your fish since they are low in nutrition and high in fat.
On the other side of the argument is that feeders are cheap and easily replaced. Additionally, people all have some sense of excitement and satisfaction watching animals hunt.
Below is a video I filmed of my friend's fish tank being fed feeder goldfish.