Question about USB HDD

Ok so I have a My Book Western Digital External USB HDD; 1TB... I notice it stays on even if the Wii is turned off... should I unplug it everynight or just let it run it's course and stay on ?

I want it to last as long as possible, but I know turning it off and on is not good for it, especially when I'm loading games every few hours I get some downloaded.

That wont occur much longer just what do you guys do? and suggest?

Thanks.

By chance do you got Wii 24hour connect on (the stand by mode when the power light is yellow)? Because if thats on then the usb are still powered.
Back when my wii was unmodded i would leave the stand by on to charge my wii remotes, but i dont use that feature any more.

Hope that helps

Thank you for that solution!