I meant they might be so closely related that you want them share the same caption and figure number and everything.
https://commons.wikimedia.org/wiki/File:Latex_example_subfig...
You can reference either the whole figure by using the label inside the figure environment, or you can reference the subfigures using labels inside the subfigure environments.
I'm not saying it doesn't work. I'm saying that if your needs are simple enough, you can get away without it.