cvs flags question

To find out what any command does use the Unix/Linux/OS X manual pages:

man cvs

Anyhow, straight from those pages under the heading "update options":

-P

         Prune empty directories.  See see node `Removing directories' in the CVS
         manual.

-A

         Reset any sticky tags, dates, or -k options.  See see node `Sticky tags'
         in the CVS manual, for more information on sticky tags/dates.

-d

         Create  any  directories that exist in the repository if they're missing
         from the working directory.  Normally, update acts only  on  directories
         and files that were already enrolled in your working directory.

         This is useful for updating directories that were created in the reposi-
         tory since the initial checkout; but it has an unfortunate side  effect.
         If  you  deliberately avoided certain directories in the repository when
         you created your working directory (either through use of a module  name
         or  by  listing  explicitly  the files and directories you wanted on the
         command line), then updating with  -d  will  create  those  directories,
         which may not be what you want

Basically it restores the checkouted branch to the latest revision.

-P prunes empty directories -A resets sticky tags -d creates directories that exists on repository but are missing locally.

See: http://ximbiot.com/cvs/wiki/CVS--Concurrent%20Versions%20System%20v1.12.12.1%3A%20Guide%20to%20CVS%20commands#SEC172