Is it wrong to leave my amplifier on all the time

I've had a few power amps that don't even have an on/off switch. Just left em on 24/7. No harm at all. But I wouldn't worry about it either way.

Either/or...

Just don't turn it off and then immediately on again without waiting 3-5 minutes.

DeKay

In other discussions,  you mention a Sugden class A amplifier.  They run hot which might impact longevity. Check with manufacturer. 

Some say, leave it on.  Some say, power it down.  Many years ago, I asked myself the same question and needed a definitive answer to the question.  So, I asked the experts, the amp manufacturers.  I was advised by the manufactures that it was perfectly ok to turn my amps on and off as many times during the day as I wished  and doing so wouldn't harm the amps one bit.  Personally, I always power down my amp when it's not going to be in use for a prolonged period of time.  Happy listening.  

I left my Class A/B amp on most of the time over 20 years and never had a problem, and I’d only turn it off if I was leaving the house for more than a couple days.  The impact on the electric bill was minimal, and it was really nice having the system warmed up and ready to go whenever I got the urge to listen.  If possible talk to the manufacturer and see what they recommend. 

Some folks will say that cycling on and off stresses the caps more than leaving an amp on all the time. I think you're fine either way really.