macOS will create local backups (space permitting) and then dump them all at once when connected to the Time Machine drive. Though of course you won't have the backups from between the last time you connected the drive to the time your computer was hosed.
I get that but what I’m saying is, why limit yourself to a “real” backup once a week? What benefit does it have to just leaving the drive plugged in?
I for one like to have some protection from crypotolockers. And power surges.
Some people use laptops, and want to move around with those laptops. Keeping an external drive connected kinda gets in the way :)