My general rule is "Feed it if it has a mouth and/or feeding tentacles". As an example, my SPS corals just have polyps and no mouth, so no feeding, just light and flow. My LPS generally have mouths and/or feeding tentacles (duncans, acans, candy canes, favia, favites), so I target feed them. Same thing with feather dusters and coco worms. I used to feed my anemones with silversides and shrimp since they have mouths, but I quit doing that about a year ago and they continue to do fine.
Hammer corals I do not feed. Here's a pic of my hammer, it has about doubled in size in almost 2 years: