Turntable cover

If TT has attached cover which swings up, what position should it be in when playing? How does it affect the sound in either position? Or should I remove the cover altogether? If I do, how do I keep the TT free of dust?
TIA for your replies. 
I too recommend it off.....use a Swiffer to keep it clean, but be very careful near the cartridge.
One option if it is possible.
Take the cover off, remove the hinges from the back of it and just place it back over the TT when not in use.
That way it still serves its purpose as a dustcover.

This is what I have done on one TT but I do not know what TT you have and if it will just sit on the plinth without hinges.
My old Dual does easily.

Might be worth looking at.
If not and you still would like a usable dustcover when not in use, you could have one made  that would sit on the plinth. Custom made on eBay about $140.
I have a Linn LP12. I'll see what I can do with the hinges.
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Thanks! I would love to see a photo of your solution.