|All electronic devices wear out. If left off they should last longer. They are rated in failure in hours of use.|
It would expose your system to possible attacks more often.
It will suck in more dust and create heat so you will have to vacuum it more often.
How hard is it to turn it off anyway? Most can be setup to hibernate. I press the off button and it is setup to hibernate. When it turns off I switch off the power strip to all the wall warts and modem and routers and everything.
I support the 'Everybody Draw Mohammed Day'. A religion doesn't deny my freedom.