For the most part, snap caps are unnecessary. I have been told that the Winchester Model 12 shouldn't be dry fired without a dummy or snap cap.
But if you remove the primer on a spent case, you might as well not use anything. The firing pin will be limited in travel by the spent primer, or snap cap.
The color of a snap cap (red) is better than to use a spent case, as we look in a chamber for "brass", Well, One could mistake a brass cartridge for a brass case dummy.
Then for feeding, We use dummys (spent primer, case, bullet) BUT this round "MUST be drilled(a hole through case) to identify a dummy round. Red stain like a marking pen helps also, but doesn't last very long.
I don't use anything but caution (no ammo present)(check chamber each time gun is picked up) And I dry fire a lot.