Not trying to start anything here...
I have two SL-12xx tables, main rig and garage rig. One's hinged, one isn't. If you listen to music at TV levels, it probably doesn't matter. But the louder you crank that volume, the more that lid resonates. And like Solman989 says, it then transfers that energy to the table. I've been removing my lids since I was a teen; it's just common sense audiophile brethren... ;-)