Gmail: what's the difference between "include text" and "respond inline"?

The title of this post pretty much summed up my question, but in case you missed it-- Gmail: what's the difference between "include text" and "respond inline"? ;-)
Thanks,
Jeff

 

Ha! Too funny-- the first link is my own question! And thanks for the second link, as I now think I understand the terminology "reply inline." I still don't understand, however, the original question-- "include text" and "reply inline" would seem to both involve putting the text you're replying to in the body of the message you are currently composing.

Is it just as simple as "If your audience was previously included on this thread, leave it alone, otherwise choose to respond inline so they can see everything up to this point"?
Thanks...