Last Saturday I played two single session pair games with my student at the WMBA sectional in Springfield Massachussetts as he tries to make life master by the summer nationals. We played in A/X (1500MP) and came in fourth overall in A (second in X) in the afternoon and second overall in A in the evening session. Our worst round in the evening was actually against the eventual winners, who only beat us by a little less than a board. Here is an interesting hand from that round, where we could have done much better than we actually did.
My partner held the West hand and was dealer. Would you preempt on this hand? Well, the flaws in preempting are the side four card major and misleading partner with your weak values (below most people's 5-11HCP range). The upside of preempting is that you do have a decent suit, and having a four card major might make the preempt more effective as sometimes the opponent with points may have only one major and cannot make a takeout double.
Many people would preempt on the grounds you preempt often at matchpoints. However, I believe that having the side four card major makes the hand more attractive as a preempt at IMPs than at matchpoints. This is because the cost of playing in the wrong suit when we have a fit in the major is larger, especially as it is unlikely that we have game with the skimpy values in this hand. For example, going plus 90 in 2 when you have plus 110 or plus 140 in hearts costs much more at matchpoints at IMPS.
Some experts believe that they would preempt with this hand but not if the major suit was spades. This is because if we have a fit in hearts, our opponents probably have a spade fit and we must try to make it as hard as possible for them to find it. However, if we have a spade fit, we can always outbid their hearts.
So would I preempt given all the pros and cons mentioned above? The answer is yes, but because of one other consideration. The most likely hands that partner will have for which it is our hand are either strong misfitting hands or strong balanced hands. If he has a misfitting hand, I can warn him immediately with a preempt. If he has a strong balanced hand, what would you respond to 1NT? You can't stayman since 2C followed by 3D would be forcing. Therefore you'd probably end up abandoning the heart suit anyway. This makes preempting a strong favorite because even if we have an 8 card heart fit (or even 9 if partner frequently opens 1NT with 5 hearts because of the rebid problem) we might not be able to play there anyway. The advantages now outweigh the disadvantages.
Anyway, back to what happened at the table. My partner decided to pass, and North opened a nebulous diamond (they were playing precision). I chose to overcall in spades now with the East hand for three reasons. First, it takes up space. Second, it's lead directing if my partner is on lead. Third, it's lead inhibiting in that if I don't hear a raise or if the opponents bid notrump confidently, I'll probably do better leading another suit. As it was, South bid clubs and North ended up declaring 3NT. I knew not to lead a spade, but in the end I decided to lead a heart as that was the "unbid suit". This did not work out well and letting the opponents make a no-play game (on a low diamond lead I still have to work out to unblock my Q if partner plays the K and returns a small one when declarer ducks) was not a good matchpoint score.
Notice what happens if partner opens 2. If North passes, I will raise to 3 and will probably buy the contract in 3 making 3 as South cannot bid 4 with so many losers vulnerable. If North doubles, I can choose to either bid 2 lead-directional with diamond support, or 3 directly. Over 2, if South bids 3 asking for a diamond stopper from North, I can now lead a diamond and set 3NT. If South bids 3, I can always bid 3 which makes or South will end up bidding 4 which goes down 1 after my partner now knows to lead a spade. Players who choose to bid 5 on the South hand if I bid 3 should not be playing with players who make a vulnerable takeout double on the North hand.
So it seems that the best possible result for EW is +110 (hard to double 4), but how do you get there without NS coming into the auction? Simple, by opening the West hand 3! In my regular partnerships, I play an opening 2 as constructive, showing 7-11HCP and a good suit. The only non-constructive preempt would be 3 and I would certainly bid it. Those players who play an aggressive preempt style should also find the 3 bid. If you will open 2 at this vulnerability with the same hand but 2-2-6-3 distribution, then this hand is actually one loser less and can be bid one level higher. To my knowledge the fourth card of a suit is not considered a loser in modern (read: optimistic) losing trick count. Someone please correct me if I'm wrong.