If you generate new addresses, new private keys for those addresses are created and hence you will need to backup your wallet.dat file everytime you do that and a transaction happens on one of those addresses to safeguard against missing funds. You can and should automate backups of the .dat file by using a cron script or if on windows create a scheduled task to backup to a secure location which only you can access to and no network access is available.

The idea with the backup here is to ensure that if a transaction happens on the addresses you generate (may it be the segwit address or legacy) you should make your backups to ensure that you have the latest wallet.dat file which contains the private keys to it.