You said it. Short term. With the correct diameter, and strong steel screw collars (? sorry I don't know the English word for those), they can seal resonably well for a few weeks, or just enough to get you to the muffler shop. And they won't be very flexible afterwards. A friend of mine did just that last year (to connect a brand-mew 408 stroker with headers, to the OEM exhaust line, approximately cut at the safety loop).

Enough to break-in the engine, drive around a little, and head to a muffler shop 80 miles away that made a custom stainless setup.
It could have held on some more.