This feels like a dumb question, so bear with me.

I just bought two new external 4TB hard drives. Is there a reason I
need a partition table on the drives, or can I just format the whole
device?

I've had some USB thumb drives without a partition table and never had
any problems with them. The disks will only be used for periodic data
backups, only on Linux.

Directly formatting the whole disk as ext4 seems slightly wrong, but
I'm not sure why I'd need the partition table.  Can someone enlighten
me?

Thanks,
--
Michael Moore