Why should you stop hand feeding?
1. Bare hands touching food or the fish could cause illness in your fish from bacteria (wear gloves or pour food into its habitat).
2. It's not natural for all types of fish to approach something that could harm them (fish tend to associate outside tank/pond movement with food so, they could associate a cat, raccoon, or something else possibly harmful to them as delivering their food source as well). If you have schooling fish that approach you for food they can manage to jump from the aquarium in the huddled excitement.
3. A predatory/carnivorous fish could end up biting you during feeding.
When should you hand feed?
1. When you can't use an auto feeder to feed your fish (not all food may fit or work in a feeder).
2. If you choose to have your fish approach you... all the time (although a fish is not a dog so why make it act like one).
3. When you have predatory/carnivorous fish that require food movement to attack/eat their prey (try to use tongs or something similar during feeding to avoid introducing bacteria and keeping yourself from getting nipped).