My primary external hard drives stay on and attached to my desktop computer, while my backup drives are only attached and on when I'm actually making backups. I use small portable hard drives for backups, and have been using powered desktop hard drives for my main drives. I just attached a 2TB SSD for my working Lightroom catalog, and it is certainly faster when uploading pictures and performing certain functions in LR and PS. I still back this up with a portable, regular spinning hard drive.
I'm sure glad I make regular backups. I recently accidentally erased a whole 3TB drive with pictures from 2015-2017. I had an exact copy on another drive, though, and was able to restore everything just fine. (whew!)
One reason I never leave my backup drives on and connected is if there was ever a lightening strike of huge power surge, I certainly don't want both my primary and backup drives destroyed at the same time.