The good news is that it looks like WhatsApp has managed to strike up a deal with Google in which WhatsApp’s backup data will no longer count towards Google Drive storage. This means that the backup data will exist outside of your quota, so if your Google Drive storage is getting pretty full and you can’t be bothered to buy more storage, then this will do the trick.
However it should be noted that this does not actually come into effect until later this year. According to WhatsApp, “Starting November 12, 2018, WhatsApp backups will no longer count towards the Google Drive storage quota. Furthermore, WhatsApp backups that haven’t been updated in more than one year will be automatically removed from Google Drive storage.”
It is unclear if there is a quota on how much backup storage users will be given, but either way this should help free up some storage space on your Google Drive come November.