If the drive is going to be used "for backup", I WOULD NOT leave it connected and running "all the time".
Just connect for backup, do backup, then disconnect.
That policy has worked well for me for 30+ years.
If you're using it for a Time Machine backup that's supposed to run every hour or so, well... I guess there's no choice?
But I don't TM. I use CarbonCopyCloner and run cloned backup updates once or twice a week.
I'm of the mind that "the longer it runs, the quicker it fails".
Others will disagree with this.
I have old hard drives that have been used only occasionally that are 10-15 years old (or older) and ... still running.