WHAT ARE THE "+,s" AND THE "-,s"  of the following feature of the ZP3

There is a standby switch allowing you to keep the unit warmed up all the time if you like.

If you keep the ZP3 in standby mode 24/7 will the tubes have a shorter life?

The 12au7 and the 12ax7 tubes run very cool (and are the most expensive due to tube rolling).  The two other tubes run hot, but are cheap to replace.

Also is the 12au7 output tube a better candidate for NOS tube rolling, than the 12ax7 tubes (for RIAA conversion)?

Thanks,

Peter