Discussion with a US skipper showed that each time they put the Seat Belt sign on, there is an extensive set of FAA-mandated SOPs that the cabin crew then have to perform around the cabin. This pi$$es them off, and as many regular travellers on mainstream US network carriers will be aware, that is something you don't do to the cabin crew of such carriers. So, it seems, for a quiet life in the hotac afterwards, just leave them on.