On or Off

Official manual:

https://www.passlabs.com/wp-content/uploads/2020/12/XP-22_om.pdf

"Leave it on or turn it off: The product is designed to be left on all the time. The
exception to this might be a case where the preamp will not be used for an extended time - in that case it can be turned off.""

I always left my Pass pre on unless I was was leaving for more then a few days or a chance weather could cause a power outage or surge.

i have a pass amp also.  the manual is not specific about leaving the front panel switch on in addition to the rear switch.  

i do leave the rear switch on but turn off the front panel switch after listening.  

On!

Mike