A third is "it uses multiple files (and the behavior can't be replicated by concatenating them)." Picking one input to still be consumed from stdin can make se

A third is "it uses multiple files (and the behavior can't be replicated by concatenating them)." Picking one input to still be consumed from stdin can make sense, though. A special case of this is config files, which are almost never read from stdin (they usually have a default location or several).