I always left my 8150 on all the time except if I wasn't going to be using it for more than a few days.
I don't really care if the insides wear out quicker, or if the power bill was slightly higher. It's a trade off I can live with to get better sound. I found it took at east a day to sound optimal. About an hour to be 95% there, 24 hours to be 99% optimal so when using it for at least a few hours a day, for me, it just made sense to leave it on permanently.
I also used to use a Gram Slee Reflex Era Gold. Not sure about burn in, as mine was secondhand, but it did take a few days from cold to sound its best.
Whether it was the equipment in absolute terms sounding better, or my human brain just perceiving it as better...who really cares.