@kohan It makes sense, it would have to be a hard-bound book (not a paper back) to stay open the same way. Or proper folder, of course.
I remember specifically there was a lot of computer documentation that came in that format and I assume it was a leftover from actual scientific and military work; the manufacturers were used to print manuals like this for computer labs and whatnot so private citizens got them too, for awhile when home computers were new.