Turntable lid up or off?

HhahahahahahaA difference in sound with the dust cover closed or removed.
SNAKE OIL!

    There is no difference.

 I have 2 SL-1200 mk2’s
one SL-1210. 
 No difference.    Just play your LP’s’ and enjoy. 
Had first SL-1200 mk2 for 30+ years. 2nd one about 5 years later.
then the SL-1210 in mid late 90’s if I remember correctly. 
    All with ortofon Arkiv and Ortofon nightclub II CONCORDE stylus.   All flawless, and no hiccups, no be,ts to tinker with.
all sound amazing.  With lid down or up,

 I can hear the cymbal and hear the drum stick hit the cymbal with the cover up, .......yeah ok....
  oh wait,....the cymbal decay is more prevalent with the cover removed as with the cover down??
ok, sure you can. 
 Just play your albums and enjoy.
don’t follow this snake oil tripe. 

VPI Classic 2  gives me  few options.  It is either on, in place, or completely off.  It is not hinged or fastened  but sits in place held by its weight. I almost always take it off.  Sometimes leave it on when rambunctious kids or dogs are visiting. 

BTW, as dust covers go, it looks OK, but has some curiously placed open spaces, like screen doors on a U-boat.  Better than nothing, but could be a tighter fit. 

Off, but dust is still a problem even with multiple HEPA air purifiers...

I ordered a custom dust cover for my table....heard a reduction of fidelity....too big for a hinge.   Off or on.....I sold it a month later.