Always worth it. Usually not too many title problems witholder cars as they are rarely bought on finance unless they are in the higher dollar bracket. But a REVS (Register of encumbered vehicles) check (free if you don't buy the certificate) can show up irregularities or possible problems.
I would also recommend ringing the RTA as well with engine, chassis and rego (if registered or has old plates) as they can tell you when it was last registered or if it can't be registered.
You can do the revs check online
http://www.revs.nsw.gov.au/
Matt