Ok guys

I take it off while playing. Simply because the hinges broke a couple of decades ago so it is either on/covered or completely removed. I do not put it back on while playing not to accidentally make some damage while positioning. It comes close to the weight, etc.

Technics SL-1200G and SL-1600MK2 both dust cover down

The manual of the VPI HW-19 MKIII recommends that "the dust cover be down when playing records. Under most circumstances this will result in cleaner sound since the cover acts as a 'shield' against acoustic feedback." And of course keep the record and stylus clean. 

Put. me in the cover on camp. SQ better.

What brand ,model turntable and cartridge ? How good it is will have a lot to do with its stability and vibration control.  I don’t know of many quality turntables with a built in lid.