I recently acquired a first edition copy of the Book of Mormon  that was about 1/4" thinner than most copies that I acquire. In fact, of the over 175 copies that I've either seen or acquired, only about five or six have been these extra-thin copies. So, here's the question, "What accounts for the difference in thickness?" Well, fortunately I have friends and experts that I can go to for answers. In this case I went to Joseph Adams (http://eidolonhouse.com), who has a degree in "printmaking" about this phenomenon. That's when he told me about "rolling machines". These rolling machines were used to flatten and consolidate the sections of a book before sewing. At the time of the printing of the first edition Book of Mormon by E. B. Grandin in Palmyra, New York, these rolling machines were mostly in use in England--they had just been invented in 1827.
Now, the big question is, "Does this 'thinness' affect the value?". Well, it depends--for the following reason: The first edition Book of Mormon has a well-known look (see http://www.pinterest.com/moonsrarebooks/first-edition-book-of-mormon-1830-pinterest/). So, when a person is looking for a first edition Book of Mormon, they usually don't want to explain why their book "doesn't look like a first edition". Having said this, I actually like finding these "thin" copies. They are typically very clean on the inside. The text in these books is usually almost always free from the brown splotches (foxing) normally seen in first editions. This leads me to believe that the leather binding--or more specifically, the chemicals used in tanning the leather--were partly, or mostly to blame for the foxing--but that's the subject of another blog. In a way, it's a trade off. So, if you would like a first edition copy of the Book of Mormon, that has a nice, clean white interior, look for one of the thin copies. The "thin" copy shown is one of ten first edition copies of the Book of Mormon currently for sale at Moon's Rare Books in Provo, Utah. These books are shown by appointment only. www.moonsrarebooks.com