Are there any circumstances under which buying a second makes sense? What are they?

Are there any circumstances under which buying a second makes sense? What are they? Is there any value here at all?

Not much value lately, but I used to buy 2nds when there was equity. They can actually be very profitable. 300k house, 200k 1st, 20k 2nd. Buy the 2nd at auction for $20k, make $20k in 3 months = 400% ROI.

Most 2nds are so underwater right now that it makes no sense.