I know as far as other QT wallets go, as long as you have the .dat file then all associated addresses will show up. No new backups are needed.
That's how i understand it, but didn't want to spout misinformation. Thanks rlhead!
Under what circumstances, if any, would a new wallet.dat backup be necessary?
The only reason I ever backup a new .dat file is if I create a new wallet. If someone knows of another reason why one would need to backup the same .dat file then I would also like to know. Maybe I've missed something. It would be good to get a definitive answer.