Turntable lid up or off?


My Pro-Ject Classic turntable came with a dust cover.  I usually spin vinyl with the cover completely removed and never closed.  Does it matter if the cover is just up or fully removed?  The ultimate test is just listening, but I cannot detect a difference between either mode (up or completely off).
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I keep it down when listening to my SL-1200 MK2. Most of my other tables don't have dust covers. Up seems like the worst option. What sounds best to you? 
@millercarbon, I just use a soft micro fiber cloth for cleaning.  My "habit" is to take the cover off and set it upside on a table on the other side of the room (sometimes I just set it on the carpet).  If I'm not using it for more than a day or so, I put the cover back on.  I'm good with a gummy or two.

@all, thanks for insights & opinions.