These envelopes are the perfect size for mailing small size books (think: fold 8 1/2 x 11 sheet in half!). I have recommended their usage over the one that is just a little bit bigger.
I am an author of hiking trail guidebooks. The books I write are up to 100 pages and and standard 8.5 x 11 pages folded in half stapled in the middle. These envelopes are the perfect size for these books. It makes packaging so much easier.
The metal clips used as part of the sealing process must be removed from each envelope or they cost you an extra 40c in postage. The USPS says that these clips get hung up in their machines and thus requires them to have to pull clasped envelopes and hand process them. Therefore it would be nice to have these without the clasps.