One dealer who sold Pass Aleph amps told me he left them on continuously, unless the shop was going to be closed for several days. He said they sounded much better that way. I would be worried about component life, and electric bills, though.
Will leaving an amp powered-up all the time...
lead to "cap saturation" that causes the amp to sound bright? A friend sez yes. A listening buddy of his left his Spectral mono's on for three months and heard a difference when they had a normal warm-up.