I use these for certificates from the church; they are always large and should not be folded. The envelope is stiff enough to keep the certificate "nice". Also I like the flap on the long side rather than the shorter end-side; easier to maneuver getting the certificate in and out.
When I don't need to impress I truly like to submit client files in these catalog envelopes looks nice and crisp and is a workable alternative to those every expensive folders.