Suppose that you are making changes to a number of configuration files. You then run a build script that generates large images, such as bootable ISO images or similar. You would like to exclude the output directories (which are going to be rebuilt every time you run the build scripts) from version control.
See this very nice post here: http://svn.haxx.se/users/archive-2005-09/0354.shtml:
Quoting from that post:
If foo3 is already under version control, and now you want it not to
be, but you still want to keep the directory in your working copy,
you can do it like this:
$ cp -rp foo3 foo3.bak $ svn rm foo3 $ svn propset svn:ignore foo3 . $ svn ci -m "Removing foo3 from version control." $ mv foo3.bak foo3 $ svn st $
foo3 is now still in the working copy, but is no longer under version
control. The svn:ignore property will prevent the directory from
annoying you in the status list.