If you want to backup metadata (such as label to transaction & address), then you need to backup your wallet file.
Even if you're not, having extra backup won't hurt, as long as you uses strong password.
Additional for this:
If you use the backup seed for recovering your wallet you can only recover addresses and transaction history but the label and contact is not included when recovering it with seed backup.
However, you can backup or export both contact and labels from Electrum.
This is just another option if you want to separate the backups from address, contacts to labels.