If its not a tube power amp then NEVER turn it off. My SMC Audio Power amp doesn't even have an on/off switch Leave your gear on, even tube pre-amps and DACS etc. They will sound better and last longer!
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!