For me, I would put it down for two reasons, the first being almost the only reason. On hard core trails I've clipped the front corner of my roll cage. This would have broken my windshield if it had been up. The other reason was cruising a nice day in the forest with the top, doors off and windshield down. So, cool factor.
I never got my M61 20mm Gatling gun mounted but that would have been the third reason. Go ahead, brake check me.