Dagnabbit! I was working on this, just as it was posted...

Anyway, my take...

Feature of many early 20th century homes, from the South well into the Midwest, Northeast and parts of California. Notable instances: The Benjamin Spock House in New Haven, Ct, and the opening chapter of Babbitt. One California house, long since defunct had, NO bedrooms, preferring the roof.

A response to the tuberculosis epidemic sweeping civilized society in the period. Since there were no antibiotics, the chief hope lay in bolstering the immune system, and lowering whatever strain there was on the lungs and bronchi. As with most fads, some decided that healthy people could benefit from this as well, and in most Germanic countries, the standard response to a cold, or anything else respiratory, is to open the window, put on a scarf, and drink a lot of herb tea. 

As with a lot of ‘alternative’ medicine, my feelings are mixed: having explained this practice to several doctors, they own that lowering exposure to allergens might help many respiratory diseases, even if the temperature outside was subfreezing, and the patient, somewhat over par. As a home treatment option, YMMV. If you have a place outside, out of the wind, you might try bundling up in a sleeping bag on a lounge chair a couple of hours a day. If nothing else, the fact you’ve got some other stimulus than daytime TV might help.

As for myself, I've often fantasized about getting an apartment with a sleeping porch. It sounds like a wonderful way to spend the Summer....