Should I turn my computer off at night?
There is no "correct" answer to this question. What matters are your preferences and values. First, we need to dismiss the old wives-tale that leaving your computer on is somehow easer on the components. This is simply not true. If you turn your computer off at night, or put it into hibernation mode, you will save energy. If you leave your computer on at night, your startup times will be shorter and you can get to work right away.
For our clients, we frequently schedule administrative updates to run overnight. These include Windows security updates and antivirus scans. If your computer is off when these events are scheduled, they will run when you next turn the computer on, which for most people is when they first sit down at their computer to catch-up on e-mail.
So, if energy conservation is most important to you, turn it off. If slow startup times are bothering you, leave it on.