If you have a tube preamp... turn it off because logic would tell you that you are putting time on the tubes.... Haven't seen any studies but it makes sense (I'm going to get 10 posts telling me I'm wrong). I've noticed that temperature and humidity makes the most difference in how my speakers sound even though those are only slight changes in my listening space.
Amp — Leave on or turn off
I always turned my Benchmark AHB2 amp off after use every night. After all, why is there an on off switch on the front panel if not to do that? Last night I accidentally left it on. This morning, when I played my first record, I couldn’t believe my ears. The same record I played last night sounded infinitely better. I tried a second record and that, too, was much better.
I know there’s a debate on the question of leaving an amp on all the time.
I now know where I stand!