How do I Feature Level Switch to turn off a map?

Sorry, but that doesn’t answer the question of when “default” is actually used.
What is the end user harrdware configuration when the “default” input will be used? Is there support for render targets other than SM4, SM5, ES2, and ES3.1?
And how can I make it so that a particular map is used only when SM4 or SM5 is selected, and turned off / not used otherwise?