While a hand is being played, the board should be on the table, and the North side should be facing North. Under Law 7, it is illegal for the board to be on a lap, on the floor, or anywhere except on the table.
There are two reasons. First, during play the players are entitled to see the vulnerability and who was dealer.
However, the main reason is to avoid misboarding. If you take a board off the table and turn it away from pointing North, you make it more likely that the board will be put back wrong way round. That means the cards will go back in the wrong slots.
Misboarding is more common than most players realise, particularly in clubs which do not enforce board discipline. It explains why other players' results on boards often seem surprising. If you misboard, the next table does not get the hand you played. The bidding sequence may change completely, because the first call will come from a different hand. Even if the final contract is the same, a different person may be on lead.
It is the established custom that N/S should take control of what happens at their table, including scoring and minding the boards. But note that all players are responsible for misboarding and E/W have a right to object if the board is taken off the table.
Copyright Michael O'Malley 2016