Join With Computer Audio

Hello, 

I use an external USB microphone, not my laptop's internal microphone.  So I set my USB microphone up in the Zoom settings and test it before each meeting.

But when I'm about to join a meeting it says something like "Join With Computer Audio?"  So my question is - when I click "Join With Computer Audio" does that mean it is reverting back to my laptop's internal microphone?  Or is it still set to the external USB microphone I have chosen?  

As a Zoom newbie I'm not entirely sure what the "Join With Computer Audio" is.  I'm just afraid that it would overide my preference for the external USB microphone and default back to the laptop internal microphone, which I don't like....   Hope someone can help me.

Many thanks! 

G