I've seen some people recommend that cement board be glued and screwed to the stud framing for wall and ceiling application.
I haven't seen this recommendation on any of the manufacturers install specs, but it seems to come up often enough in DIY and other web communities as a way to keep the board fixed and rigid with the framing.
Yes, but not just for rigidity.
Cement board is made of, well, cement - and cement is brittle.
When you screw the cement board in you create a pressure point or stress point. Even though the board is screwed in with lots and lots of screws, each screw hole is a stress point prone to breakage.
By gluing the board as well as screwing, you ensure that a much larger surface area of the board ultimately bonds to the wood (as the glue cures) - which means that if a single stress point fails, it won't matter, because the glue holds the board tight where the screw hole may have failed.
