Here's a case in point:
Some readers will say that the South hand could start with a negative double and then bid clubs. I prefer to play so-called "negative free bids" (which, by the way, fit hand-in-glove with cooperative doubles) so that particular sequence becomes a game-force. But even playing standard, don't you think that starting with a double distorts this hand significantly by marginalizing a good six-card suit?
Do I hear any dissenters? Yes, of course I do. Some of you may feel that with such an "obvious" double, North should be able to double 3♠ for penalties? But think about it for a moment. How frequently is that going to come up? At the three level, after the opponents have made a Law-of-total-tricks raise, the player sitting under the bidder will rarely have a holding that is good enough to double with confidence. On this kind of auction, it's much more likely that it is our hand but we haven't yet found a fit. Mel Colchamiro has a great name for a double by North here: the "balance-of-power" double. "BOP 'em," he says. You might argue that the 3♣ bid, which is so highly informative, should trigger penalty doubles. That is a valid point of view. Nevertheless, the opponents are jamming our auction and we have not yet had a good chance for either of us to show four hearts. Transfer two of those diamonds into the heart suit and we have a decent shot at game, yet the auction so far would have proceeded just the same.
In general, it is my opinion that, playing against reasonably sane opponents who have announced a good fit, it is more useful to be able to find our best fit than to increase their penalty. And, what if you have a great hand and a stack of trumps and are prevented from doubling? It may be a blessing when partner is bust. Those situations usually work better when the hand sitting over declarer has the trump stack while partner has the entries. That avoids opening leader being end-played at every turn.
Yes, but how can you make a takeout double when there is only one suit to take out into? I know some of you are thinking this. The point here is that it is not a pure "takeout" double. It's a cooperative double showing that we have the balance of power and asking partner his opinion. One of the suits that partner might favor is the one that's already been bid and doubled – a penalty pass.
Going back to our example hand, the more observant of you may have noticed that we can make 3NT, despite having only 22 hcp. That's another possibility that I didn't mention before – taking the double out into a notrump game. Indeed, this is one of those fairly rare hands where notrump plays better than any suit. Next to notrump our best fit is diamonds where we can take eight tricks. But how much better it is to score 400 instead of 100?
For more blogs on this interesting topic, see for example Single-suit cooperative doubles or Using double to find out about fit.