If your wallet.dat file was created with a version of Bitcoin Core prior to Bitcoin Core 0.13.0, the wallet.dat will only be good for the 100 addresses that you use after the backup is made. That includes change addresses, so it typically means 100 transactions before you have to backup again.

With wallets created with Bitcoin Core 0.13.0 and later, the wallet.dat will have the necessary information to derive all of your future addresses since it is a deterministic wallet. However this is not enough as you won't know how many addresses it should generate and look transactions for when you restore. You still should make periodic backups.