I think they were more common with balloon built houses, too -- a little extra rigidity and a draft-and-fire break in those loooong cavities.

I can't remember for sure whether my folks' 1933 house had any in walls we demolished... but that's not very indicative of anything, since it was built by a guy who was clearly cutting corners! (There was a 'header' that didn't actually go all the way across a door, for one thing).