Why (and How) I Still Use Time Machine to Back Up My Mac

Automatically start a Time Machine backup when you plug in the drive and dismount the drive when the backup is complete.
Ars Technica

Why is TIme Machine not doing a complete backup?

I'm trying to create a TM backup to restore from. Even though it is a completely new drive and TM is set to defaults, it is only backing up 1/2 the data. The drive is 50GB full. TM is backing up only ...