Do we have to keep updating our board according to solution given in repository... just a query ..
(because my phpbb3 hacked 2 times, so don't want anything that now)
No, you only need to upgrade when a version is released (eg 1.6.1, 2.0 etc). You shouldn't use any SVN code unless it's a temporary fix to a problem that will be solved.
If you really need a bug fix that's in the repository you're free to use it, but we wouldn't be able to support you if you were using full SVN code as it's not considered stable and hasn't been 'signed off' as fit for release.