They can work for catfish, bass or panfish. About anything goes. Channel cat like smelly baits. Flat heads like live baits. I have best luck with turkey livers tipped with shrimp or crawdads.
Small bluegill work pretty good.
I usually cut them in 2. Some people have good luck with stink baits. Personally, I haven't. I've also fished those very smelly shad sides from the jars but have never caught anything on them. Of course, it's hard to beat a plain ol' night crawler.