Name some of these cases.

I think it's mostly a "thought exercise", but here's a treatment looking at the costs of commuting to SF from Las Vegas: http://mobile.businessinsider.com/its-cheaper-to-commute-fro...

As that article points out, you're looking at 2 hours of commuting each way with that.

I assure you, you can find a cheaper total cost of living + commuting within 2 hours of SF by car.

My point was simply how absurd this is, not that it's a practical alternative.

Some employees at UCSF do this -- They can get on a 7-on/7-off schedule, fly in from somewhere more reasonable (often Denver or somewhere in the Midwest), stay on a couch for a week, earn a SF salary then fly back to a $1,500/month mortgage somewhere else.

'Stay on a couch for a week' - pretty large pre-requisite here..

I don't disagree, but they often have coworkers who work opposite shifts (7am - 7pm vs. 7pm - 7am) so they can share an apartment space without running into each other too much.