Even with solid state gear, there is some debate about the disadvantages, in terms of equipment longevity/reliability about leaving gear on 24/7. First, there is a possibility, however remote, of failure that could cause a fire. Second, there is the issue of lightning strike or other powerline calamity (some people unplug gear completely when not in use to prevent that kind of damage). The third concern has to do with heat--high heat will shorten the life of any component. If you look at specifications for parts, such as resistors, transistors and capacitors, the lifetime projections show shortened life expectancy for higher heat conditions. Some people will say that certain parts, such as electrolytic capacitors are actually better off being charged all the time, but, the flip side of that is the heat issue. One should check with the manufacturer about this sort of thing if ultimate longevity is a big concern; in terms of sound, fully warmed up gear, whether tube or solid state, sounds better.
