I guess I am in the middle on this one. My african cichlids do not get live foods as they really need more vegetable matter in their diet to prevent bloat. The Jack Dempsey, on the other hand, gets the occasional night crawler as a treat. He loves them.
I have fed brine shrimp to tropicals, fry (livebearers and African cichlids, protein seems to aid in growth in these), dwarf puffers, and SA/CA cichlids. These were a treat with pellet and flake being the main staples.
Years ago, I had a mud dog. It was like a salamander, I haven't seen one since I had mine and for the most part they ate freeze dried tubifex. Occasionally, they would stop eating and the only way to get them started again was to use a feeder fish. I would buy minnows from a bait store and put them in a hospital tank with mercurochrome (not available anymore in most places because of mercury but a good all around illness treatment for fish, used for cuts, scrapes like iodine in humans). This would ensure their health before feeding them to my pets. I would not ever use a minnow or feeder goldfish that had not been properly quarantined and treated.
I also had newts.....one of them is my avatar. They ate meal worms and wouldn't eat anything else.
So yes, I do use live foods if necessary but I feel that for the majority of fish, they are not necessary. Most fish can be adapted to eat pellets and/or flake and this should provide balanced nutrition for them.