"errors can be checked and corrected and the PC knows whats what"
If the computer is off, then what to you mean ? How can it check things.
I leave my computer on permanently, the a restart or a couple of hours downtime every couple of days. But this is more to allow it to download and run programs overnight.
I cannot imagine how shutting down the computer will harm it, I would tend to say some downtime to allow the CPU to cool is ideal.