For a number of reasons I have always kept my computer [laptop] on, 24 7's. Now I can just as well turn it off at night. I have been told that the number one cause of hardware failures for electronics in general is solder joint failure. Temperature changes help to encourage problems if bad joints are present. Maybe over time and many cycles, temperature changes are highly significant for loose contacts? I assume that leaving the computer on would minimize temperature fluctuations. Next, I suspect that for computers the cooling fans would tend to fail relatively frequently - a function of the on time and a root cause for CPU and power supply failures? So, to what extent is the foregoing reasoning true, and in order to achieve the greatest life expectancy should I leave my computer on or turn it off at night?