Source: Let the opponents play in a vulnerable part-score
ALTHOUGH (as we saw in Click here) vulnerability is irrelevant at match-point duplicate in an uncontested auction, it is hugely relevant in the competitive arena. And it is not only your vulnerability that matters – it is also the opponents’.
Take this hand: 
A J 7 5 2 
Q 3 2 
Q 8 5 2 
7 after the bidding has gone 1NT – Pass – Pass to you. Should you protect with a bid of 2? Say you are non-vulnerable. It is certainly very tempting – after all you don’t really fancy defending 1NT on a likely opening club lead from partner. So do you or don’t you? Me – I don’t have enough information. I know that my side is non-vulnerable but I haven’t been told whether or not my oppo – nents are non-vulnerable – almost as important. This deal shows what I mean:
Should East pass or bid 2?
At the table East bid 2. He bought a useful dummy, and played well. Winning South’s small club lead with dummy’s king, he ran the ten of hearts at trick two. South won the ace and, with no good play, led a second club. Winning the ace and discarding a diamond, declarerled a second heart. North won the king and persevered with a third club. Declarer ruffed and led a low trump to the queen (South ducking), a trump back to the ace, and a third trump, pleased to see the 3-3 split (throwing the last club from dummy). He ruffed the club return (a diamond going from dummy), cashed the queen of hearts, then led towards the king of diamonds, with the winning thirteenth heart waiting to be enjoyed. All South could win was the ace of diamonds. 2 +1 and +140. East awaited the traveller/Bridgemate with interest – surely his bold bidding and accurate play had earned a near-top . . .
Nope – a near bottom!
Can you see why? At other tables the less venturesome Easts had let South play 1NT, which fares miserably. Without torturing you with the details, all declarer is likely to win is one spade, two hearts, one diamond and one club. The dreaded -200. A row of +200s to East-West meant that our East’s +140 scored just 32% of the matchpoints. It was the opponents’ vulnerability that had been all-important here. Had they been non-vulnerable, then +140 would have been a near-top (compared with lots of +100 defending 1NT down two). Not so with North-South vulnerable.