This is just my guess, but if left on 24/7, I bet you'd chew through amplifier output tubes every six months. With normal 1-4 hour listening sessions then leaving the amps off when not in use I imagine you'd get 2 years out of a set of output tubes.
Tubes don;t like being turned on and off (like everything else), but letting then burn 168 hours a week with little use is is sort of silly. This applies to amp output tubes. line level tubes like those found in preamps and phono stages generally last longer and cost less to replace (uses less electricity and heat your house less), so you will generally see people suggest that you keep them on (if not 24/7, then at least during the periods when you listen the most, like weekends, holidays, etc)
Tubes don;t like being turned on and off (like everything else), but letting then burn 168 hours a week with little use is is sort of silly. This applies to amp output tubes. line level tubes like those found in preamps and phono stages generally last longer and cost less to replace (uses less electricity and heat your house less), so you will generally see people suggest that you keep them on (if not 24/7, then at least during the periods when you listen the most, like weekends, holidays, etc)